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	$79.38	4.358%	$82.8394	$82.84	$82.85	$82.80
Purchase #2	$49.31	10.650%	$54.5615	$54.56	$54.55	$54.60
Purchase #3	$171.51	10.606%	$189.7004	$189.70	$189.70	$189.70
Purchase #4	$107.64	10.224%	$118.6451	$118.65	$118.65	$118.60
Purchase #5	$24.89	5.570%	$26.2764	$26.28	$26.30	$26.30
Purchase #6	$56.91	4.463%	$59.4499	$59.45	$59.45	$59.40
Purchase #7	$104.73	7.650%	$112.7418	$112.74	$112.75	$112.70
7 purchase totals =	$594.37		$644.2145	$644.22	$644.25	$644.10