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 $139.50   8.372%   $151.1789   $151.18   $151.20   $151.20  
  Purchase #2 $119.53   10.233%   $131.7615   $131.76   $131.75   $131.80  
  Purchase #3 $77.97   8.797%   $84.829   $84.83   $84.85   $84.80  
  Purchase #4 $84.53   9.291%   $92.3837   $92.38   $92.40   $92.40  
  Purchase #5 $166.81   4.621%   $174.5183   $174.52   $174.50   $174.50  
  Purchase #6 $129.84   10.251%   $143.1499   $143.15   $143.15   $143.10  
  Purchase #7 $24.50   3.279%   $25.3034   $25.30   $25.30   $25.30  
  7 purchase totals = $742.68       $803.1247   $803.12   $803.15   $803.10