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 $161.77   9.173%   $176.6092   $176.61   $176.60   $176.60  
  Purchase #2 $160.88   9.114%   $175.5426   $175.54   $175.55   $175.50  
  Purchase #3 $88.51   11.729%   $98.8913   $98.89   $98.90   $98.90  
  Purchase #4 $217.29   9.352%   $237.611   $237.61   $237.60   $237.60  
  Purchase #5 $9.63   13.163%   $10.8976   $10.90   $10.90   $10.90  
  Purchase #6 $154.27   8.338%   $167.133   $167.13   $167.15   $167.10  
  Purchase #7 $42.83   10.455%   $47.3079   $47.31   $47.30   $47.30  
  7 purchase totals = $835.18       $913.9926   $913.99   $914.00   $913.90