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 $115.62   9.504%   $126.6085   $126.61   $126.60   $126.60  
  Purchase #2 $206.44   11.710%   $230.6141   $230.61   $230.60   $230.60  
  Purchase #3 $67.50   11.534%   $75.2855   $75.29   $75.30   $75.30  
  Purchase #4 $179.87   9.869%   $197.6214   $197.62   $197.60   $197.60  
  Purchase #5 $167.49   13.217%   $189.6272   $189.63   $189.65   $189.60  
  Purchase #6 $237.35   6.611%   $253.0412   $253.04   $253.05   $253.00  
  Purchase #7 $154.83   12.437%   $174.0862   $174.09   $174.10   $174.10  
  7 purchase totals = $1,129.10       $1,246.8841   $1,246.89   $1,246.90   $1,246.80