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 $34.46   6.387%   $36.661   $36.66   $36.65   $36.70  
  Purchase #2 $244.32   10.670%   $270.3889   $270.39   $270.40   $270.40  
  Purchase #3 $44.95   5.634%   $47.4825   $47.48   $47.50   $47.50  
  Purchase #4 $229.31   5.871%   $242.7728   $242.77   $242.75   $242.80  
  Purchase #5 $121.33   5.378%   $127.8551   $127.86   $127.85   $127.90  
  Purchase #6 $25.85   10.295%   $28.5113   $28.51   $28.50   $28.50  
  Purchase #7 $84.26   9.209%   $92.0195   $92.02   $92.00   $92.00  
  7 purchase totals = $784.48       $845.6911   $845.69   $845.65   $845.80