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 $56.71   11.662%   $63.3235   $63.32   $63.30   $63.30  
  Purchase #2 $29.95   11.757%   $33.4712   $33.47   $33.45   $33.50  
  Purchase #3 $95.42   10.413%   $105.3561   $105.36   $105.35   $105.40  
  Purchase #4 $162.81   12.685%   $183.4624   $183.46   $183.45   $183.50  
  Purchase #5 $228.82   6.825%   $244.437   $244.44   $244.45   $244.40  
  Purchase #6 $94.52   3.523%   $97.8499   $97.85   $97.85   $97.80  
  Purchase #7 $195.80   8.168%   $211.7929   $211.79   $211.80   $211.80  
  7 purchase totals = $864.03       $939.6930   $939.69   $939.65   $939.70