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 $175.68   11.279%   $195.4949   $195.49   $195.50   $195.50  
  Purchase #2 $121.66   9.379%   $133.0705   $133.07   $133.05   $133.10  
  Purchase #3 $43.96   11.449%   $48.993   $48.99   $49.00   $49.00  
  Purchase #4 $248.73   11.772%   $278.0105   $278.01   $278.00   $278.00  
  Purchase #5 $50.49   8.115%   $54.5873   $54.59   $54.60   $54.60  
  Purchase #6 $119.31   11.827%   $133.4208   $133.42   $133.40   $133.40  
  Purchase #7 $106.92   5.652%   $112.9631   $112.96   $112.95   $113.00  
  7 purchase totals = $866.75       $956.5401   $956.53   $956.50   $956.60