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 $205.75   13.703%   $233.9439   $233.94   $233.95   $233.90  
  Purchase #2 $70.55   8.422%   $76.4917   $76.49   $76.50   $76.50  
  Purchase #3 $87.33   6.680%   $93.1636   $93.16   $93.15   $93.20  
  Purchase #4 $108.61   4.652%   $113.6625   $113.66   $113.65   $113.70  
  Purchase #5 $243.44   13.845%   $277.1443   $277.14   $277.15   $277.10  
  Purchase #6 $44.90   8.120%   $48.5459   $48.55   $48.55   $48.50  
  Purchase #7 $103.57   11.112%   $115.0787   $115.08   $115.10   $115.10  
  7 purchase totals = $864.15       $958.0306   $958.02   $958.05   $958.00