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 $205.52   11.593%   $229.3459   $229.35   $229.35   $229.30  
  Purchase #2 $243.81   7.726%   $262.6468   $262.65   $262.65   $262.60  
  Purchase #3 $207.32   7.643%   $223.1655   $223.17   $223.15   $223.20  
  Purchase #4 $113.33   6.224%   $120.3837   $120.38   $120.40   $120.40  
  Purchase #5 $123.64   13.503%   $140.3351   $140.34   $140.35   $140.30  
  Purchase #6 $237.62   5.202%   $249.981   $249.98   $250.00   $250.00  
  Purchase #7 $170.69   9.477%   $186.8663   $186.87   $186.85   $186.90  
  7 purchase totals = $1,301.93       $1,412.7243   $1,412.74   $1,412.75   $1,412.70