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	$95.32	4.608%	$99.7123	$99.71	$99.70	$99.70
Purchase #2	$203.79	13.583%	$231.4708	$231.47	$231.45	$231.50
Purchase #3	$232.76	12.612%	$262.1157	$262.12	$262.10	$262.10
Purchase #4	$50.73	11.320%	$56.4726	$56.47	$56.45	$56.50
Purchase #5	$37.57	10.212%	$41.4066	$41.41	$41.40	$41.40
Purchase #6	$155.98	7.288%	$167.3478	$167.35	$167.35	$167.30
Purchase #7	$77.70	13.834%	$88.449	$88.45	$88.45	$88.40
7 purchase totals =	$853.85		$946.9748	$946.98	$946.90	$946.90