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 $42.84   9.768%   $47.0246   $47.02   $47.00   $47.00  
  Purchase #2 $162.90   9.797%   $178.8593   $178.86   $178.85   $178.90  
  Purchase #3 $169.50   13.140%   $191.7723   $191.77   $191.75   $191.80  
  Purchase #4 $243.74   7.671%   $262.4373   $262.44   $262.45   $262.40  
  Purchase #5 $88.42   11.287%   $98.4   $98.40   $98.40   $98.40  
  Purchase #6 $215.37   8.761%   $234.2386   $234.24   $234.25   $234.20  
  Purchase #7 $19.64   10.780%   $21.7572   $21.76   $21.75   $21.80  
  7 purchase totals = $942.41       $1,034.4893   $1,034.49   $1,034.45   $1,034.50