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 $62.78   7.166%   $67.2788   $67.28   $67.30   $67.30  
  Purchase #2 $245.41   13.266%   $277.9661   $277.97   $277.95   $278.00  
  Purchase #3 $146.27   6.686%   $156.0496   $156.05   $156.05   $156.00  
  Purchase #4 $91.83   10.138%   $101.1397   $101.14   $101.15   $101.10  
  Purchase #5 $166.43   7.549%   $178.9938   $178.99   $179.00   $179.00  
  Purchase #6 $249.66   9.602%   $273.6324   $273.63   $273.65   $273.60  
  Purchase #7 $140.70   6.121%   $149.3122   $149.31   $149.30   $149.30  
  7 purchase totals = $1,103.08       $1,204.3726   $1,204.37   $1,204.40   $1,204.30