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 $90.70   5.862%   $96.0168   $96.02   $96.00   $96.00  
  Purchase #2 $199.68   8.487%   $216.6268   $216.63   $216.65   $216.60  
  Purchase #3 $110.49   6.692%   $117.884   $117.88   $117.90   $117.90  
  Purchase #4 $61.87   11.760%   $69.1459   $69.15   $69.15   $69.10  
  Purchase #5 $57.96   3.306%   $59.8762   $59.88   $59.90   $59.90  
  Purchase #6 $126.76   12.411%   $142.4922   $142.49   $142.50   $142.50  
  Purchase #7 $27.40   7.779%   $29.5314   $29.53   $29.55   $29.50  
  7 purchase totals = $674.86       $731.5733   $731.58   $731.65   $731.50