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 $40.86   12.612%   $46.0133   $46.01   $46.00   $46.00  
  Purchase #2 $249.94   11.190%   $277.9083   $277.91   $277.90   $277.90  
  Purchase #3 $10.34   5.290%   $10.887   $10.89   $10.90   $10.90  
  Purchase #4 $208.51   4.239%   $217.3487   $217.35   $217.35   $217.30  
  Purchase #5 $60.32   11.450%   $67.2266   $67.23   $67.25   $67.20  
  Purchase #6 $222.63   7.723%   $239.8237   $239.82   $239.80   $239.80  
  Purchase #7 $127.88   5.401%   $134.7868   $134.79   $134.80   $134.80  
  7 purchase totals = $920.48       $993.9944   $994.00   $994.00   $993.90