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	$165.74	13.510%	$188.1315	$188.13	$188.15	$188.10
Purchase #2	$91.32	13.418%	$103.5733	$103.57	$103.55	$103.60
Purchase #3	$33.90	11.454%	$37.7829	$37.78	$37.80	$37.80
Purchase #4	$71.65	9.768%	$78.6488	$78.65	$78.65	$78.60
Purchase #5	$82.52	11.569%	$92.0667	$92.07	$92.05	$92.10
Purchase #6	$60.43	11.445%	$67.3462	$67.35	$67.35	$67.30
Purchase #7	$12.96	11.861%	$14.4972	$14.50	$14.50	$14.50
7 purchase totals =	$518.52		$582.0466	$582.05	$582.05	$582.00