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 $63.79   6.801%   $68.1284   $68.13   $68.15   $68.10  
  Purchase #2 $190.93   9.569%   $209.2001   $209.20   $209.20   $209.20  
  Purchase #3 $180.27   12.498%   $202.8001   $202.80   $202.80   $202.80  
  Purchase #4 $8.85   6.341%   $9.4112   $9.41   $9.40   $9.40  
  Purchase #5 $30.88   5.475%   $32.5707   $32.57   $32.55   $32.60  
  Purchase #6 $45.76   3.108%   $47.1822   $47.18   $47.20   $47.20  
  Purchase #7 $241.79   13.358%   $274.0883   $274.09   $274.10   $274.10  
  7 purchase totals = $762.27       $843.3810   $843.38   $843.40   $843.40