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 $111.78   11.179%   $124.2759   $124.28   $124.30   $124.30  
  Purchase #2 $185.74   4.387%   $193.8884   $193.89   $193.90   $193.90  
  Purchase #3 $18.54   10.474%   $20.4819   $20.48   $20.50   $20.50  
  Purchase #4 $166.62   12.122%   $186.8177   $186.82   $186.80   $186.80  
  Purchase #5 $178.86   11.797%   $199.9601   $199.96   $199.95   $200.00  
  Purchase #6 $126.69   8.460%   $137.408   $137.41   $137.40   $137.40  
  Purchase #7 $177.30   8.293%   $192.0035   $192.00   $192.00   $192.00  
  7 purchase totals = $965.53       $1,054.8355   $1,054.84   $1,054.85   $1,054.90