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 $54.45   13.417%   $61.7556   $61.76   $61.75   $61.80  
  Purchase #2 $107.28   8.874%   $116.8   $116.80   $116.80   $116.80  
  Purchase #3 $182.62   4.814%   $191.4113   $191.41   $191.40   $191.40  
  Purchase #4 $23.54   6.304%   $25.024   $25.02   $25.00   $25.00  
  Purchase #5 $64.64   8.813%   $70.3367   $70.34   $70.35   $70.30  
  Purchase #6 $189.78   8.642%   $206.1808   $206.18   $206.20   $206.20  
  Purchase #7 $250.66   5.299%   $263.9425   $263.94   $263.95   $263.90  
  7 purchase totals = $872.97       $935.4509   $935.45   $935.45   $935.40