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 $63.34   13.656%   $71.9897   $71.99   $72.00   $72.00  
  Purchase #2 $130.99   10.766%   $145.0924   $145.09   $145.10   $145.10  
  Purchase #3 $154.42   9.553%   $169.1717   $169.17   $169.15   $169.20  
  Purchase #4 $114.73   10.322%   $126.5724   $126.57   $126.55   $126.60  
  Purchase #5 $164.53   3.713%   $170.639   $170.64   $170.65   $170.60  
  Purchase #6 $149.93   8.184%   $162.2003   $162.20   $162.20   $162.20  
  Purchase #7 $133.58   9.582%   $146.3796   $146.38   $146.40   $146.40  
  7 purchase totals = $911.52       $992.0451   $992.04   $992.05   $992.10