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 $245.77   5.454%   $259.1743   $259.17   $259.15   $259.20  
  Purchase #2 $175.36   4.137%   $182.6146   $182.61   $182.60   $182.60  
  Purchase #3 $14.72   7.831%   $15.8727   $15.87   $15.85   $15.90  
  Purchase #4 $132.73   13.307%   $150.3924   $150.39   $150.40   $150.40  
  Purchase #5 $44.72   6.698%   $47.7153   $47.72   $47.70   $47.70  
  Purchase #6 $126.72   7.821%   $136.6308   $136.63   $136.65   $136.60  
  Purchase #7 $206.46   12.257%   $231.7658   $231.77   $231.75   $231.80  
  7 purchase totals = $946.48       $1,024.1659   $1,024.16   $1,024.10   $1,024.20