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 $49.94   13.238%   $56.5511   $56.55   $56.55   $56.60  
  Purchase #2 $142.87   4.598%   $149.4392   $149.44   $149.45   $149.40  
  Purchase #3 $68.71   6.267%   $73.0161   $73.02   $73.00   $73.00  
  Purchase #4 $83.68   9.526%   $91.6514   $91.65   $91.65   $91.70  
  Purchase #5 $184.64   4.822%   $193.5433   $193.54   $193.55   $193.50  
  Purchase #6 $136.30   11.392%   $151.8273   $151.83   $151.85   $151.80  
  Purchase #7 $56.77   13.318%   $64.3306   $64.33   $64.35   $64.30  
  7 purchase totals = $722.91       $780.3590   $780.36   $780.40   $780.30