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 $23.72   6.601%   $25.2858   $25.29   $25.30   $25.30  
  Purchase #2 $56.49   5.222%   $59.4399   $59.44   $59.45   $59.40  
  Purchase #3 $109.78   8.723%   $119.3561   $119.36   $119.35   $119.40  
  Purchase #4 $94.76   8.516%   $102.8298   $102.83   $102.85   $102.80  
  Purchase #5 $45.49   5.562%   $48.0202   $48.02   $48.00   $48.00  
  Purchase #6 $187.45   13.611%   $212.9638   $212.96   $212.95   $213.00  
  Purchase #7 $207.74   9.468%   $227.4088   $227.41   $227.40   $227.40  
  7 purchase totals = $725.43       $795.3044   $795.31   $795.30   $795.30