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 $213.63   10.618%   $236.3132   $236.31   $236.30   $236.30  
  Purchase #2 $144.36   8.719%   $156.9467   $156.95   $156.95   $156.90  
  Purchase #3 $111.42   9.205%   $121.6762   $121.68   $121.70   $121.70  
  Purchase #4 $27.34   6.172%   $29.0274   $29.03   $29.05   $29.00  
  Purchase #5 $234.82   6.427%   $249.9119   $249.91   $249.90   $249.90  
  Purchase #6 $48.73   7.333%   $52.3034   $52.30   $52.30   $52.30  
  Purchase #7 $61.85   5.606%   $65.3173   $65.32   $65.30   $65.30  
  7 purchase totals = $842.15       $911.4961   $911.50   $911.50   $911.40