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 $96.94   8.278%   $104.9647   $104.96   $104.95   $105.00  
  Purchase #2 $121.51   11.207%   $135.1276   $135.13   $135.15   $135.10  
  Purchase #3 $9.29   10.406%   $10.2567   $10.26   $10.25   $10.30  
  Purchase #4 $148.93   7.157%   $159.5889   $159.59   $159.60   $159.60  
  Purchase #5 $122.68   12.417%   $137.9132   $137.91   $137.90   $137.90  
  Purchase #6 $208.66   13.559%   $236.9522   $236.95   $236.95   $237.00  
  Purchase #7 $202.38   10.484%   $223.5975   $223.60   $223.60   $223.60  
  7 purchase totals = $910.39       $1,008.4008   $1,008.40   $1,008.40   $1,008.50