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 $205.98   8.862%   $224.2339   $224.23   $224.25   $224.20  
  Purchase #2 $104.39   11.122%   $116.0003   $116.00   $116.00   $116.00  
  Purchase #3 $19.54   9.172%   $21.3322   $21.33   $21.35   $21.30  
  Purchase #4 $168.39   13.183%   $190.5889   $190.59   $190.60   $190.60  
  Purchase #5 $235.94   7.361%   $253.3075   $253.31   $253.30   $253.30  
  Purchase #6 $20.83   12.206%   $23.3725   $23.37   $23.35   $23.40  
  Purchase #7 $33.85   12.393%   $38.045   $38.05   $38.05   $38.00  
  7 purchase totals = $788.92       $866.8803   $866.88   $866.90   $866.80