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 $55.94   7.342%   $60.0471   $60.05   $60.05   $60.00  
  Purchase #2 $159.98   5.392%   $168.6061   $168.61   $168.60   $168.60  
  Purchase #3 $170.43   13.575%   $193.5659   $193.57   $193.55   $193.60  
  Purchase #4 $123.82   7.691%   $133.343   $133.34   $133.35   $133.30  
  Purchase #5 $92.51   8.546%   $100.4159   $100.42   $100.40   $100.40  
  Purchase #6 $109.95   13.848%   $125.1759   $125.18   $125.20   $125.20  
  Purchase #7 $192.60   4.562%   $201.3864   $201.39   $201.40   $201.40  
  7 purchase totals = $905.23       $982.5403   $982.56   $982.55   $982.50