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 $67.84   13.272%   $76.8437   $76.84   $76.85   $76.80  
  Purchase #2 $136.97   10.186%   $150.9218   $150.92   $150.90   $150.90  
  Purchase #3 $55.78   6.446%   $59.3756   $59.38   $59.40   $59.40  
  Purchase #4 $208.47   9.465%   $228.2017   $228.20   $228.20   $228.20  
  Purchase #5 $200.91   5.396%   $211.7511   $211.75   $211.75   $211.80  
  Purchase #6 $47.65   6.661%   $50.824   $50.82   $50.80   $50.80  
  Purchase #7 $178.39   5.321%   $187.8821   $187.88   $187.90   $187.90  
  7 purchase totals = $896.01       $965.8000   $965.79   $965.80   $965.80