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 $143.69   10.821%   $159.2387   $159.24   $159.25   $159.20  
  Purchase #2 $77.93   8.430%   $84.4995   $84.50   $84.50   $84.50  
  Purchase #3 $121.71   11.847%   $136.129   $136.13   $136.15   $136.10  
  Purchase #4 $195.43   8.195%   $211.4455   $211.45   $211.45   $211.40  
  Purchase #5 $224.79   8.634%   $244.1984   $244.20   $244.20   $244.20  
  Purchase #6 $46.78   13.786%   $53.2291   $53.23   $53.25   $53.20  
  Purchase #7 $116.96   7.319%   $125.5203   $125.52   $125.50   $125.50  
  7 purchase totals = $927.29       $1,014.2605   $1,014.27   $1,014.30   $1,014.10