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 $208.62   11.557%   $232.7302   $232.73   $232.75   $232.70  
  Purchase #2 $64.25   7.319%   $68.9525   $68.95   $68.95   $69.00  
  Purchase #3 $208.25   8.342%   $225.6222   $225.62   $225.60   $225.60  
  Purchase #4 $105.74   3.236%   $109.1617   $109.16   $109.15   $109.20  
  Purchase #5 $247.30   10.508%   $273.2863   $273.29   $273.30   $273.30  
  Purchase #6 $183.74   12.671%   $207.0217   $207.02   $207.00   $207.00  
  Purchase #7 $178.41   4.712%   $186.8167   $186.82   $186.80   $186.80  
  7 purchase totals = $1,196.31       $1,303.5913   $1,303.59   $1,303.55   $1,303.60