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 $54.80   6.371%   $58.2913   $58.29   $58.30   $58.30  
  Purchase #2 $162.51   7.347%   $174.4496   $174.45   $174.45   $174.40  
  Purchase #3 $222.78   9.761%   $244.5256   $244.53   $244.55   $244.50  
  Purchase #4 $37.30   11.519%   $41.5966   $41.60   $41.60   $41.60  
  Purchase #5 $68.86   4.594%   $72.0234   $72.02   $72.00   $72.00  
  Purchase #6 $26.50   13.644%   $30.1157   $30.12   $30.10   $30.10  
  Purchase #7 $236.68   13.439%   $268.4874   $268.49   $268.50   $268.50  
  7 purchase totals = $809.43       $889.4896   $889.50   $889.50   $889.40