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 $219.43   10.267%   $241.9589   $241.96   $241.95   $242.00  
  Purchase #2 $234.81   11.398%   $261.5736   $261.57   $261.55   $261.60  
  Purchase #3 $202.91   11.655%   $226.5592   $226.56   $226.55   $226.60  
  Purchase #4 $137.60   4.589%   $143.9145   $143.91   $143.90   $143.90  
  Purchase #5 $121.35   13.267%   $137.4495   $137.45   $137.45   $137.40  
  Purchase #6 $125.43   4.567%   $131.1584   $131.16   $131.15   $131.20  
  Purchase #7 $95.47   3.695%   $98.9976   $99.00   $99.00   $99.00  
  7 purchase totals = $1,137.00       $1,241.6117   $1,241.61   $1,241.55   $1,241.70