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 $164.98   9.466%   $180.597   $180.60   $180.60   $180.60  
  Purchase #2 $23.52   10.535%   $25.9978   $26.00   $26.00   $26.00  
  Purchase #3 $211.94   9.800%   $232.7101   $232.71   $232.70   $232.70  
  Purchase #4 $140.52   7.675%   $151.3049   $151.30   $151.30   $151.30  
  Purchase #5 $242.75   9.658%   $266.1948   $266.19   $266.20   $266.20  
  Purchase #6 $93.83   8.349%   $101.6639   $101.66   $101.65   $101.70  
  Purchase #7 $7.73   5.552%   $8.1592   $8.16   $8.15   $8.20  
  7 purchase totals = $885.27       $966.6277   $966.62   $966.60   $966.70