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 $58.91   11.585%   $65.7347   $65.73   $65.75   $65.70  
  Purchase #2 $66.25   8.183%   $71.6712   $71.67   $71.65   $71.70  
  Purchase #3 $112.36   12.262%   $126.1376   $126.14   $126.15   $126.10  
  Purchase #4 $154.46   3.168%   $159.3533   $159.35   $159.35   $159.40  
  Purchase #5 $92.36   13.501%   $104.8295   $104.83   $104.85   $104.80  
  Purchase #6 $62.26   5.422%   $65.6357   $65.64   $65.65   $65.60  
  Purchase #7 $106.83   3.298%   $110.3533   $110.35   $110.35   $110.40  
  7 purchase totals = $653.43       $703.7153   $703.71   $703.75   $703.70