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 $246.27   7.533%   $264.8215   $264.82   $264.80   $264.80  
  Purchase #2 $131.63   9.281%   $143.8466   $143.85   $143.85   $143.80  
  Purchase #3 $87.61   5.112%   $92.0886   $92.09   $92.10   $92.10  
  Purchase #4 $124.92   7.168%   $133.8743   $133.87   $133.85   $133.90  
  Purchase #5 $60.64   7.719%   $65.3208   $65.32   $65.30   $65.30  
  Purchase #6 $91.86   4.493%   $95.9873   $95.99   $96.00   $96.00  
  Purchase #7 $164.90   12.299%   $185.1811   $185.18   $185.20   $185.20  
  7 purchase totals = $907.83       $981.1202   $981.12   $981.10   $981.10