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 $33.70   7.874%   $36.3535   $36.35   $36.35   $36.40  
  Purchase #2 $205.56   13.667%   $233.6539   $233.65   $233.65   $233.70  
  Purchase #3 $64.43   5.623%   $68.0529   $68.05   $68.05   $68.10  
  Purchase #4 $97.72   6.736%   $104.3024   $104.30   $104.30   $104.30  
  Purchase #5 $13.28   8.583%   $14.4198   $14.42   $14.40   $14.40  
  Purchase #6 $209.68   7.836%   $226.1105   $226.11   $226.10   $226.10  
  Purchase #7 $17.86   9.459%   $19.5494   $19.55   $19.55   $19.50  
  7 purchase totals = $642.23       $702.4424   $702.43   $702.40   $702.50