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 $245.34   9.246%   $268.0241   $268.02   $268.00   $268.00  
  Purchase #2 $125.65   3.681%   $130.2752   $130.28   $130.30   $130.30  
  Purchase #3 $236.70   4.413%   $247.1456   $247.15   $247.15   $247.10  
  Purchase #4 $84.57   4.653%   $88.505   $88.51   $88.50   $88.50  
  Purchase #5 $184.96   9.105%   $201.8006   $201.80   $201.80   $201.80  
  Purchase #6 $193.27   9.203%   $211.0566   $211.06   $211.05   $211.10  
  Purchase #7 $62.76   13.268%   $71.087   $71.09   $71.10   $71.10  
  7 purchase totals = $1,133.25       $1,217.8941   $1,217.91   $1,217.90   $1,217.90