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 $236.77   3.852%   $245.8904   $245.89   $245.90   $245.90  
  Purchase #2 $191.96   4.202%   $200.0262   $200.03   $200.05   $200.00  
  Purchase #3 $229.81   8.585%   $249.5392   $249.54   $249.55   $249.50  
  Purchase #4 $33.59   5.701%   $35.505   $35.51   $35.50   $35.50  
  Purchase #5 $242.41   6.629%   $258.4794   $258.48   $258.50   $258.50  
  Purchase #6 $190.53   10.814%   $211.1339   $211.13   $211.15   $211.10  
  Purchase #7 $84.66   11.636%   $94.511   $94.51   $94.50   $94.50  
  7 purchase totals = $1,209.73       $1,295.0851   $1,295.09   $1,295.15   $1,295.00