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 $168.33   10.146%   $185.4088   $185.41   $185.40   $185.40  
  Purchase #2 $198.73   8.360%   $215.3438   $215.34   $215.35   $215.30  
  Purchase #3 $239.96   11.456%   $267.4498   $267.45   $267.45   $267.40  
  Purchase #4 $161.38   3.269%   $166.6555   $166.66   $166.65   $166.70  
  Purchase #5 $77.92   13.553%   $88.4805   $88.48   $88.50   $88.50  
  Purchase #6 $208.41   11.519%   $232.4167   $232.42   $232.40   $232.40  
  Purchase #7 $161.80   5.796%   $171.1779   $171.18   $171.20   $171.20  
  7 purchase totals = $1,216.53       $1,326.9330   $1,326.94   $1,326.95   $1,326.90