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 $110.98   11.574%   $123.8248   $123.82   $123.80   $123.80  
  Purchase #2 $209.75   10.793%   $232.3883   $232.39   $232.40   $232.40  
  Purchase #3 $51.56   7.802%   $55.5827   $55.58   $55.60   $55.60  
  Purchase #4 $40.93   11.706%   $45.7213   $45.72   $45.70   $45.70  
  Purchase #5 $142.65   5.617%   $150.6627   $150.66   $150.65   $150.70  
  Purchase #6 $28.86   5.278%   $30.3832   $30.38   $30.40   $30.40  
  Purchase #7 $117.72   6.205%   $125.0245   $125.02   $125.00   $125.00  
  7 purchase totals = $702.45       $763.5875   $763.57   $763.55   $763.60