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 $156.44   10.603%   $173.0273   $173.03   $173.05   $173.00  
  Purchase #2 $77.49   9.213%   $84.6292   $84.63   $84.65   $84.60  
  Purchase #3 $191.27   5.181%   $201.1797   $201.18   $201.20   $201.20  
  Purchase #4 $226.31   4.527%   $236.5551   $236.56   $236.55   $236.60  
  Purchase #5 $117.95   13.787%   $134.2118   $134.21   $134.20   $134.20  
  Purchase #6 $147.32   13.204%   $166.7721   $166.77   $166.75   $166.80  
  Purchase #7 $231.98   10.863%   $257.18   $257.18   $257.20   $257.20  
  7 purchase totals = $1,148.76       $1,253.5552   $1,253.56   $1,253.60   $1,253.60