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 $61.71   7.658%   $66.4358   $66.44   $66.45   $66.40  
  Purchase #2 $183.71   9.747%   $201.6162   $201.62   $201.60   $201.60  
  Purchase #3 $117.30   4.350%   $122.4026   $122.40   $122.40   $122.40  
  Purchase #4 $244.38   12.707%   $275.4334   $275.43   $275.45   $275.40  
  Purchase #5 $44.42   6.678%   $47.3864   $47.39   $47.40   $47.40  
  Purchase #6 $11.72   8.231%   $12.6847   $12.68   $12.70   $12.70  
  Purchase #7 $189.45   5.225%   $199.3488   $199.35   $199.35   $199.30  
  7 purchase totals = $852.69       $925.3079   $925.31   $925.35   $925.20