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 $69.94   7.655%   $75.2939   $75.29   $75.30   $75.30  
  Purchase #2 $117.91   13.622%   $133.9717   $133.97   $133.95   $134.00  
  Purchase #3 $23.65   9.701%   $25.9443   $25.94   $25.95   $25.90  
  Purchase #4 $212.72   11.233%   $236.6148   $236.61   $236.60   $236.60  
  Purchase #5 $110.30   6.782%   $117.7805   $117.78   $117.80   $117.80  
  Purchase #6 $154.75   4.829%   $162.2229   $162.22   $162.20   $162.20  
  Purchase #7 $107.66   5.349%   $113.4187   $113.42   $113.40   $113.40  
  7 purchase totals = $796.93       $865.2468   $865.23   $865.20   $865.20