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 $125.49   13.126%   $141.9618   $141.96   $141.95   $142.00  
  Purchase #2 $84.51   4.852%   $88.6104   $88.61   $88.60   $88.60  
  Purchase #3 $102.97   10.237%   $113.511   $113.51   $113.50   $113.50  
  Purchase #4 $177.68   4.843%   $186.285   $186.29   $186.30   $186.30  
  Purchase #5 $173.85   3.642%   $180.1816   $180.18   $180.20   $180.20  
  Purchase #6 $66.64   12.323%   $74.852   $74.85   $74.85   $74.90  
  Purchase #7 $30.38   11.112%   $33.7558   $33.76   $33.75   $33.80  
  7 purchase totals = $761.52       $819.1576   $819.16   $819.15   $819.30