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	$169.76	13.791%	$193.1716	$193.17	$193.15	$193.20
Purchase #2	$180.42	7.287%	$193.5672	$193.57	$193.55	$193.60
Purchase #3	$122.55	4.103%	$127.5782	$127.58	$127.60	$127.60
Purchase #4	$147.91	5.119%	$155.4815	$155.48	$155.50	$155.50
Purchase #5	$221.98	4.476%	$231.9158	$231.92	$231.90	$231.90
Purchase #6	$80.87	11.581%	$90.2356	$90.24	$90.25	$90.20
Purchase #7	$91.35	11.600%	$101.9466	$101.95	$101.95	$101.90
7 purchase totals =	$1,014.84		$1,093.8965	$1,093.91	$1,093.90	$1,093.90