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 $54.84   3.115%   $56.5483   $56.55   $56.55   $56.50  
  Purchase #2 $244.94   4.800%   $256.6971   $256.70   $256.70   $256.70  
  Purchase #3 $247.44   6.579%   $263.7191   $263.72   $263.70   $263.70  
  Purchase #4 $86.46   5.537%   $91.2473   $91.25   $91.25   $91.20  
  Purchase #5 $178.62   9.148%   $194.9602   $194.96   $194.95   $195.00  
  Purchase #6 $157.91   5.362%   $166.3771   $166.38   $166.40   $166.40  
  Purchase #7 $146.86   4.477%   $153.4349   $153.43   $153.45   $153.40  
  7 purchase totals = $1,117.07       $1,182.9840   $1,182.99   $1,183.00   $1,182.90