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 $38.34   7.143%   $41.0786   $41.08   $41.10   $41.10  
  Purchase #2 $213.38   3.738%   $221.3561   $221.36   $221.35   $221.40  
  Purchase #3 $236.50   4.305%   $246.6813   $246.68   $246.70   $246.70  
  Purchase #4 $211.48   10.502%   $233.6896   $233.69   $233.70   $233.70  
  Purchase #5 $229.43   13.408%   $260.192   $260.19   $260.20   $260.20  
  Purchase #6 $134.66   11.387%   $149.9937   $149.99   $150.00   $150.00  
  Purchase #7 $38.53   10.447%   $42.5552   $42.56   $42.55   $42.60  
  7 purchase totals = $1,102.32       $1,195.5465   $1,195.55   $1,195.60   $1,195.70