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 $202.73   5.164%   $213.199   $213.20   $213.20   $213.20  
  Purchase #2 $36.98   5.204%   $38.9044   $38.90   $38.90   $38.90  
  Purchase #3 $164.69   12.192%   $184.769   $184.77   $184.75   $184.80  
  Purchase #4 $138.38   5.585%   $146.1085   $146.11   $146.10   $146.10  
  Purchase #5 $121.34   12.301%   $136.266   $136.27   $136.25   $136.30  
  Purchase #6 $163.92   8.369%   $177.6385   $177.64   $177.65   $177.60  
  Purchase #7 $79.34   13.169%   $89.7883   $89.79   $89.80   $89.80  
  7 purchase totals = $907.38       $986.6737   $986.68   $986.65   $986.70