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	$108.73	12.107%	$121.8939	$121.89	$121.90	$121.90
Purchase #2	$60.95	10.711%	$67.4784	$67.48	$67.50	$67.50
Purchase #3	$48.30	4.246%	$50.3508	$50.35	$50.35	$50.40
Purchase #4	$133.87	10.745%	$148.2543	$148.25	$148.25	$148.30
Purchase #5	$140.50	5.681%	$148.4818	$148.48	$148.50	$148.50
Purchase #6	$170.76	8.446%	$185.1824	$185.18	$185.20	$185.20
Purchase #7	$22.86	8.629%	$24.8326	$24.83	$24.85	$24.80
7 purchase totals =	$685.97		$746.4742	$746.46	$746.55	$746.60