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 $188.67   3.286%   $194.8697   $194.87   $194.85   $194.90  
  Purchase #2 $121.87   9.252%   $133.1454   $133.15   $133.15   $133.10  
  Purchase #3 $64.56   10.211%   $71.1522   $71.15   $71.15   $71.20  
  Purchase #4 $156.68   9.295%   $171.2434   $171.24   $171.25   $171.20  
  Purchase #5 $146.99   11.177%   $163.4191   $163.42   $163.40   $163.40  
  Purchase #6 $153.47   3.526%   $158.8814   $158.88   $158.90   $158.90  
  Purchase #7 $120.90   8.639%   $131.3446   $131.34   $131.35   $131.30  
  7 purchase totals = $953.14       $1,024.0558   $1,024.05   $1,024.05   $1,024.00