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 $214.93   13.777%   $244.5409   $244.54   $244.55   $244.50  
  Purchase #2 $203.78   6.400%   $216.8219   $216.82   $216.80   $216.80  
  Purchase #3 $139.44   11.599%   $155.6136   $155.61   $155.60   $155.60  
  Purchase #4 $125.32   5.538%   $132.2602   $132.26   $132.25   $132.30  
  Purchase #5 $217.96   5.451%   $229.841   $229.84   $229.85   $229.80  
  Purchase #6 $26.42   4.233%   $27.5384   $27.54   $27.55   $27.50  
  Purchase #7 $206.67   5.284%   $217.5904   $217.59   $217.60   $217.60  
  7 purchase totals = $1,134.52       $1,224.2064   $1,224.20   $1,224.20   $1,224.10