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 $216.44   12.817%   $244.1811   $244.18   $244.20   $244.20  
  Purchase #2 $62.82   7.770%   $67.7011   $67.70   $67.70   $67.70  
  Purchase #3 $53.38   12.535%   $60.0712   $60.07   $60.05   $60.10  
  Purchase #4 $75.56   12.689%   $85.1478   $85.15   $85.15   $85.10  
  Purchase #5 $97.87   7.106%   $104.8246   $104.82   $104.80   $104.80  
  Purchase #6 $146.26   9.578%   $160.2688   $160.27   $160.25   $160.30  
  Purchase #7 $193.91   7.313%   $208.0906   $208.09   $208.10   $208.10  
  7 purchase totals = $846.24       $930.2852   $930.28   $930.25   $930.30