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 $22.87   10.342%   $25.2352   $25.24   $25.25   $25.20  
  Purchase #2 $224.61   5.481%   $236.9209   $236.92   $236.90   $236.90  
  Purchase #3 $96.75   7.862%   $104.3565   $104.36   $104.35   $104.40  
  Purchase #4 $204.61   10.173%   $225.425   $225.43   $225.45   $225.40  
  Purchase #5 $132.53   4.247%   $138.1585   $138.16   $138.15   $138.20  
  Purchase #6 $180.44   10.594%   $199.5558   $199.56   $199.55   $199.60  
  Purchase #7 $230.27   13.836%   $262.1302   $262.13   $262.15   $262.10  
  7 purchase totals = $1,092.08       $1,191.7821   $1,191.80   $1,191.80   $1,191.80