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 $67.41   9.723%   $73.9643   $73.96   $73.95   $74.00  
  Purchase #2 $59.29   4.545%   $61.9847   $61.98   $62.00   $62.00  
  Purchase #3 $236.85   10.733%   $262.2711   $262.27   $262.25   $262.30  
  Purchase #4 $182.49   13.291%   $206.7447   $206.74   $206.75   $206.70  
  Purchase #5 $23.58   5.260%   $24.8203   $24.82   $24.80   $24.80  
  Purchase #6 $159.67   6.700%   $170.3679   $170.37   $170.35   $170.40  
  Purchase #7 $6.80   7.437%   $7.3057   $7.31   $7.30   $7.30  
  7 purchase totals = $736.09       $807.4587   $807.45   $807.40   $807.50