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 $239.85   7.575%   $258.0186   $258.02   $258.00   $258.00  
  Purchase #2 $106.47   4.539%   $111.3027   $111.30   $111.30   $111.30  
  Purchase #3 $23.83   9.138%   $26.0076   $26.01   $26.00   $26.00  
  Purchase #4 $115.72   7.380%   $124.2601   $124.26   $124.25   $124.30  
  Purchase #5 $76.71   6.147%   $81.4254   $81.43   $81.45   $81.40  
  Purchase #6 $132.42   11.429%   $147.5543   $147.55   $147.55   $147.60  
  Purchase #7 $178.32   5.219%   $187.6265   $187.63   $187.65   $187.60  
  7 purchase totals = $873.32       $936.1952   $936.20   $936.20   $936.20