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 $169.31   13.560%   $192.2684   $192.27   $192.25   $192.30  
  Purchase #2 $121.59   8.748%   $132.2267   $132.23   $132.25   $132.20  
  Purchase #3 $146.29   8.478%   $158.6925   $158.69   $158.70   $158.70  
  Purchase #4 $223.51   6.223%   $237.419   $237.42   $237.40   $237.40  
  Purchase #5 $239.47   6.720%   $255.5624   $255.56   $255.55   $255.60  
  Purchase #6 $132.60   3.179%   $136.8154   $136.82   $136.80   $136.80  
  Purchase #7 $188.70   13.226%   $213.6575   $213.66   $213.65   $213.70  
  7 purchase totals = $1,221.47       $1,326.6419   $1,326.65   $1,326.60   $1,326.70