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	$50.77	12.762%	$57.2493	$57.25	$57.25	$57.20
Purchase #2	$122.32	5.345%	$128.858	$128.86	$128.85	$128.90
Purchase #3	$175.82	3.215%	$181.4726	$181.47	$181.45	$181.50
Purchase #4	$155.84	4.562%	$162.9494	$162.95	$162.95	$162.90
Purchase #5	$11.50	7.631%	$12.3776	$12.38	$12.40	$12.40
Purchase #6	$33.80	11.626%	$37.7296	$37.73	$37.75	$37.70
Purchase #7	$104.48	5.428%	$110.1512	$110.15	$110.15	$110.20
7 purchase totals =	$654.53		$690.7877	$690.79	$690.80	$690.80