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 $115.26   9.471%   $126.1763   $126.18   $126.20   $126.20  
  Purchase #2 $113.31   3.520%   $117.2985   $117.30   $117.30   $117.30  
  Purchase #3 $159.86   7.534%   $171.9039   $171.90   $171.90   $171.90  
  Purchase #4 $135.95   9.566%   $148.955   $148.96   $148.95   $149.00  
  Purchase #5 $149.86   9.398%   $163.9438   $163.94   $163.95   $163.90  
  Purchase #6 $8.93   6.584%   $9.518   $9.52   $9.50   $9.50  
  Purchase #7 $77.56   9.448%   $84.8879   $84.89   $84.90   $84.90  
  7 purchase totals = $760.73       $822.6834   $822.69   $822.70   $822.70