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 $236.46   13.449%   $268.2615   $268.26   $268.25   $268.30  
  Purchase #2 $194.60   6.343%   $206.9435   $206.94   $206.95   $206.90  
  Purchase #3 $123.25   9.672%   $135.1707   $135.17   $135.15   $135.20  
  Purchase #4 $207.77   8.109%   $224.6181   $224.62   $224.60   $224.60  
  Purchase #5 $143.45   8.270%   $155.3133   $155.31   $155.30   $155.30  
  Purchase #6 $58.50   6.649%   $62.3897   $62.39   $62.40   $62.40  
  Purchase #7 $174.55   13.330%   $197.8175   $197.82   $197.80   $197.80  
  7 purchase totals = $1,138.58       $1,250.5143   $1,250.51   $1,250.45   $1,250.50