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	$49.30	9.437%	$53.9524	$53.95	$53.95	$54.00
Purchase #2	$152.73	6.378%	$162.4711	$162.47	$162.45	$162.50
Purchase #3	$63.77	4.320%	$66.5249	$66.52	$66.50	$66.50
Purchase #4	$245.45	7.258%	$263.2648	$263.26	$263.25	$263.30
Purchase #5	$129.48	3.363%	$133.8344	$133.83	$133.85	$133.80
Purchase #6	$149.34	8.788%	$162.464	$162.46	$162.45	$162.50
Purchase #7	$134.49	12.803%	$151.7088	$151.71	$151.70	$151.70
7 purchase totals =	$924.56		$994.2204	$994.20	$994.15	$994.30