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 $41.88   13.361%   $47.4756   $47.48   $47.50   $47.50  
  Purchase #2 $180.36   10.619%   $199.5124   $199.51   $199.50   $199.50  
  Purchase #3 $235.83   13.688%   $268.1104   $268.11   $268.10   $268.10  
  Purchase #4 $171.78   10.312%   $189.494   $189.49   $189.50   $189.50  
  Purchase #5 $90.36   8.679%   $98.2023   $98.20   $98.20   $98.20  
  Purchase #6 $154.38   9.539%   $169.1063   $169.11   $169.10   $169.10  
  Purchase #7 $71.91   6.861%   $76.8437   $76.84   $76.85   $76.80  
  7 purchase totals = $946.50       $1,048.7447   $1,048.74   $1,048.75   $1,048.70