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 $65.86   11.636%   $73.5235   $73.52   $73.50   $73.50  
  Purchase #2 $73.76   10.239%   $81.3123   $81.31   $81.30   $81.30  
  Purchase #3 $126.73   3.538%   $131.2137   $131.21   $131.20   $131.20  
  Purchase #4 $143.41   3.483%   $148.405   $148.41   $148.40   $148.40  
  Purchase #5 $226.41   8.874%   $246.5016   $246.50   $246.50   $246.50  
  Purchase #6 $13.96   9.491%   $15.2849   $15.28   $15.30   $15.30  
  Purchase #7 $120.95   10.204%   $133.2917   $133.29   $133.30   $133.30  
  7 purchase totals = $771.08       $829.5327   $829.52   $829.50   $829.50