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 $219.63   13.658%   $249.6271   $249.63   $249.65   $249.60  
  Purchase #2 $17.76   7.343%   $19.0641   $19.06   $19.05   $19.10  
  Purchase #3 $121.89   6.854%   $130.2443   $130.24   $130.25   $130.20  
  Purchase #4 $63.55   12.406%   $71.434   $71.43   $71.45   $71.40  
  Purchase #5 $177.74   6.186%   $188.735   $188.74   $188.75   $188.70  
  Purchase #6 $126.40   8.504%   $137.1491   $137.15   $137.15   $137.10  
  Purchase #7 $34.30   7.668%   $36.9301   $36.93   $36.95   $36.90  
  7 purchase totals = $761.27       $833.1837   $833.18   $833.25   $833.00