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 $217.99   6.552%   $232.2727   $232.27   $232.25   $232.30  
  Purchase #2 $103.46   11.573%   $115.4334   $115.43   $115.45   $115.40  
  Purchase #3 $234.64   4.314%   $244.7624   $244.76   $244.75   $244.80  
  Purchase #4 $207.70   4.393%   $216.8243   $216.82   $216.80   $216.80  
  Purchase #5 $140.87   11.207%   $156.6573   $156.66   $156.65   $156.70  
  Purchase #6 $248.61   6.437%   $264.613   $264.61   $264.60   $264.60  
  Purchase #7 $105.94   13.175%   $119.8976   $119.90   $119.90   $119.90  
  7 purchase totals = $1,259.21       $1,350.4607   $1,350.45   $1,350.40   $1,350.50