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 $246.72   6.627%   $263.0701   $263.07   $263.05   $263.10  
  Purchase #2 $148.38   13.645%   $168.6265   $168.63   $168.65   $168.60  
  Purchase #3 $159.63   5.410%   $168.266   $168.27   $168.25   $168.30  
  Purchase #4 $65.51   5.772%   $69.2912   $69.29   $69.30   $69.30  
  Purchase #5 $27.78   5.345%   $29.2648   $29.26   $29.25   $29.30  
  Purchase #6 $136.92   5.473%   $144.4136   $144.41   $144.40   $144.40  
  Purchase #7 $202.40   13.480%   $229.6835   $229.68   $229.70   $229.70  
  7 purchase totals = $987.34       $1,072.6157   $1,072.61   $1,072.60   $1,072.70