Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $164.37   13.159%   $185.9994   $186.00   $186.00   $186.00  
  Purchase #2 $183.70   12.209%   $206.1279   $206.13   $206.15   $206.10  
  Purchase #3 $202.42   12.236%   $227.1881   $227.19   $227.20   $227.20  
  Purchase #4 $96.77   12.242%   $108.6166   $108.62   $108.60   $108.60  
  Purchase #5 $226.79   6.239%   $240.9394   $240.94   $240.95   $240.90  
  Purchase #6 $211.36   8.682%   $229.7103   $229.71   $229.70   $229.70  
  Purchase #7 $210.46   7.740%   $226.7496   $226.75   $226.75   $226.70  
  7 purchase totals = $1,295.87       $1,425.3313   $1,425.34   $1,425.35   $1,425.20