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 $239.89   11.519%   $267.5229   $267.52   $267.50   $267.50  
  Purchase #2 $125.35   9.134%   $136.7995   $136.80   $136.80   $136.80  
  Purchase #3 $245.59   7.650%   $264.3776   $264.38   $264.40   $264.40  
  Purchase #4 $53.90   11.754%   $60.2354   $60.24   $60.25   $60.20  
  Purchase #5 $130.82   6.685%   $139.5653   $139.57   $139.55   $139.60  
  Purchase #6 $250.74   7.128%   $268.6127   $268.61   $268.60   $268.60  
  Purchase #7 $123.46   8.251%   $133.6467   $133.65   $133.65   $133.60  
  7 purchase totals = $1,169.75       $1,270.7601   $1,270.77   $1,270.75   $1,270.70