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 $153.49   10.522%   $169.6402   $169.64   $169.65   $169.60  
  Purchase #2 $149.53   8.850%   $162.7634   $162.76   $162.75   $162.80  
  Purchase #3 $54.34   8.143%   $58.7649   $58.76   $58.75   $58.80  
  Purchase #4 $70.82   8.105%   $76.56   $76.56   $76.55   $76.60  
  Purchase #5 $160.33   9.661%   $175.8195   $175.82   $175.80   $175.80  
  Purchase #6 $203.41   4.328%   $212.2136   $212.21   $212.20   $212.20  
  Purchase #7 $116.56   9.664%   $127.8244   $127.82   $127.80   $127.80  
  7 purchase totals = $908.48       $983.5860   $983.57   $983.50   $983.60