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 $21.86   13.720%   $24.8592   $24.86   $24.85   $24.90  
  Purchase #2 $51.63   8.422%   $55.9783   $55.98   $56.00   $56.00  
  Purchase #3 $96.28   10.234%   $106.1333   $106.13   $106.15   $106.10  
  Purchase #4 $79.61   9.305%   $87.0177   $87.02   $87.00   $87.00  
  Purchase #5 $54.31   3.572%   $56.25   $56.25   $56.25   $56.30  
  Purchase #6 $197.85   9.302%   $216.254   $216.25   $216.25   $216.30  
  Purchase #7 $130.79   13.843%   $148.8953   $148.90   $148.90   $148.90  
  7 purchase totals = $632.33       $695.3878   $695.39   $695.40   $695.50