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 $52.92   3.369%   $54.7029   $54.70   $54.70   $54.70  
  Purchase #2 $15.95   4.193%   $16.6188   $16.62   $16.60   $16.60  
  Purchase #3 $101.52   13.725%   $115.4536   $115.45   $115.45   $115.50  
  Purchase #4 $14.96   10.842%   $16.582   $16.58   $16.60   $16.60  
  Purchase #5 $223.96   7.676%   $241.1512   $241.15   $241.15   $241.20  
  Purchase #6 $90.63   12.272%   $101.7521   $101.75   $101.75   $101.80  
  Purchase #7 $16.59   9.318%   $18.1359   $18.14   $18.15   $18.10  
  7 purchase totals = $516.53       $564.3965   $564.39   $564.40   $564.50