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 $22.41   13.581%   $25.4535   $25.45   $25.45   $25.50  
  Purchase #2 $153.73   9.468%   $168.2852   $168.29   $168.30   $168.30  
  Purchase #3 $25.40   13.630%   $28.862   $28.86   $28.85   $28.90  
  Purchase #4 $20.64   11.222%   $22.9562   $22.96   $22.95   $23.00  
  Purchase #5 $61.35   12.161%   $68.8108   $68.81   $68.80   $68.80  
  Purchase #6 $140.60   5.174%   $147.8746   $147.87   $147.85   $147.90  
  Purchase #7 $17.76   13.492%   $20.1562   $20.16   $20.15   $20.20  
  7 purchase totals = $441.89       $482.3985   $482.40   $482.35   $482.60