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 $245.65   6.503%   $261.6246   $261.62   $261.60   $261.60  
  Purchase #2 $47.29   6.786%   $50.4991   $50.50   $50.50   $50.50  
  Purchase #3 $162.76   7.303%   $174.6464   $174.65   $174.65   $174.60  
  Purchase #4 $143.90   10.564%   $159.1016   $159.10   $159.10   $159.10  
  Purchase #5 $106.28   6.832%   $113.541   $113.54   $113.55   $113.50  
  Purchase #6 $164.42   5.809%   $173.9712   $173.97   $173.95   $174.00  
  Purchase #7 $23.51   6.731%   $25.0925   $25.09   $25.10   $25.10  
  7 purchase totals = $893.81       $958.4764   $958.47   $958.45   $958.40