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 $161.57   13.471%   $183.3351   $183.34   $183.35   $183.30  
  Purchase #2 $74.25   10.574%   $82.1012   $82.10   $82.10   $82.10  
  Purchase #3 $119.91   9.873%   $131.7487   $131.75   $131.75   $131.70  
  Purchase #4 $164.46   9.620%   $180.2811   $180.28   $180.30   $180.30  
  Purchase #5 $42.69   10.544%   $47.1912   $47.19   $47.20   $47.20  
  Purchase #6 $37.70   11.165%   $41.9092   $41.91   $41.90   $41.90  
  Purchase #7 $120.57   13.296%   $136.601   $136.60   $136.60   $136.60  
  7 purchase totals = $721.15       $803.1675   $803.17   $803.20   $803.10