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 $239.33   11.542%   $266.9535   $266.95   $266.95   $267.00  
  Purchase #2 $58.33   5.678%   $61.642   $61.64   $61.65   $61.60  
  Purchase #3 $178.42   7.556%   $191.9014   $191.90   $191.90   $191.90  
  Purchase #4 $219.90   12.575%   $247.5524   $247.55   $247.55   $247.60  
  Purchase #5 $154.75   3.634%   $160.3736   $160.37   $160.35   $160.40  
  Purchase #6 $194.38   6.216%   $206.4627   $206.46   $206.45   $206.50  
  Purchase #7 $212.62   9.304%   $232.4022   $232.40   $232.40   $232.40  
  7 purchase totals = $1,257.73       $1,367.2878   $1,367.27   $1,367.25   $1,367.40