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 $26.62   7.272%   $28.5558   $28.56   $28.55   $28.60  
  Purchase #2 $141.39   10.644%   $156.4396   $156.44   $156.45   $156.40  
  Purchase #3 $230.35   9.143%   $251.4109   $251.41   $251.40   $251.40  
  Purchase #4 $8.76   12.615%   $9.8651   $9.87   $9.85   $9.90  
  Purchase #5 $119.79   13.741%   $136.2503   $136.25   $136.25   $136.30  
  Purchase #6 $233.42   12.453%   $262.4878   $262.49   $262.50   $262.50  
  Purchase #7 $109.95   7.518%   $118.216   $118.22   $118.20   $118.20  
  7 purchase totals = $870.28       $963.2255   $963.24   $963.20   $963.30