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 $225.49   3.211%   $232.7305   $232.73   $232.75   $232.70  
  Purchase #2 $63.83   12.181%   $71.6051   $71.61   $71.60   $71.60  
  Purchase #3 $53.25   8.205%   $57.6192   $57.62   $57.60   $57.60  
  Purchase #4 $194.43   13.872%   $221.4013   $221.40   $221.40   $221.40  
  Purchase #5 $14.85   7.555%   $15.9719   $15.97   $15.95   $16.00  
  Purchase #6 $182.42   11.134%   $202.7306   $202.73   $202.75   $202.70  
  Purchase #7 $248.60   7.789%   $267.9635   $267.96   $267.95   $268.00  
  7 purchase totals = $982.87       $1,070.0221   $1,070.02   $1,070.00   $1,070.00