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 $71.80   5.163%   $75.507   $75.51   $75.50   $75.50  
  Purchase #2 $56.37   5.776%   $59.6259   $59.63   $59.65   $59.60  
  Purchase #3 $241.54   5.562%   $254.9745   $254.97   $254.95   $255.00  
  Purchase #4 $114.69   4.163%   $119.4645   $119.46   $119.45   $119.50  
  Purchase #5 $47.97   7.732%   $51.679   $51.68   $51.70   $51.70  
  Purchase #6 $222.99   5.306%   $234.8218   $234.82   $234.80   $234.80  
  Purchase #7 $145.63   12.765%   $164.2197   $164.22   $164.20   $164.20  
  7 purchase totals = $900.99       $960.2924   $960.29   $960.25   $960.30