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	$69.69	13.543%	$79.1281	$79.13	$79.15	$79.10
Purchase #2	$53.89	11.175%	$59.9122	$59.91	$59.90	$59.90
Purchase #3	$86.65	6.591%	$92.3611	$92.36	$92.35	$92.40
Purchase #4	$33.32	5.569%	$35.1756	$35.18	$35.20	$35.20
Purchase #5	$235.35	4.441%	$245.8019	$245.80	$245.80	$245.80
Purchase #6	$35.66	10.339%	$39.3469	$39.35	$39.35	$39.30
Purchase #7	$69.40	13.383%	$78.6878	$78.69	$78.70	$78.70
7 purchase totals =	$583.96		$630.4136	$630.42	$630.45	$630.40