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 $107.55   10.663%   $119.0181   $119.02   $119.00   $119.00  
  Purchase #2 $244.67   6.232%   $259.9178   $259.92   $259.90   $259.90  
  Purchase #3 $210.94   11.219%   $234.6054   $234.61   $234.60   $234.60  
  Purchase #4 $83.84   3.845%   $87.0636   $87.06   $87.05   $87.10  
  Purchase #5 $94.42   10.856%   $104.6702   $104.67   $104.65   $104.70  
  Purchase #6 $104.28   6.850%   $111.4232   $111.42   $111.40   $111.40  
  Purchase #7 $45.30   10.729%   $50.1602   $50.16   $50.15   $50.20  
  7 purchase totals = $891.00       $966.8585   $966.86   $966.75   $966.90