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	$20.89	3.428%	$21.6061	$21.61	$21.60	$21.60
Purchase #2	$149.99	4.337%	$156.4951	$156.50	$156.50	$156.50
Purchase #3	$59.94	9.729%	$65.7716	$65.77	$65.75	$65.80
Purchase #4	$220.94	4.725%	$231.3794	$231.38	$231.40	$231.40
Purchase #5	$155.41	4.482%	$162.3755	$162.38	$162.40	$162.40
Purchase #6	$140.74	7.704%	$151.5826	$151.58	$151.60	$151.60
Purchase #7	$37.74	5.334%	$39.7531	$39.75	$39.75	$39.80
7 purchase totals =	$785.65		$828.9634	$828.97	$829.00	$829.10