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 $65.41   12.770%   $73.7629   $73.76   $73.75   $73.80  
  Purchase #2 $219.39   13.239%   $248.435   $248.44   $248.45   $248.40  
  Purchase #3 $28.74   12.779%   $32.4127   $32.41   $32.40   $32.40  
  Purchase #4 $51.75   11.266%   $57.5802   $57.58   $57.60   $57.60  
  Purchase #5 $185.66   12.463%   $208.7988   $208.80   $208.80   $208.80  
  Purchase #6 $18.85   5.234%   $19.8366   $19.84   $19.85   $19.80  
  Purchase #7 $232.49   9.217%   $253.9186   $253.92   $253.90   $253.90  
  7 purchase totals = $802.29       $894.7448   $894.75   $894.75   $894.70