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	$80.81	10.253%	$89.0954	$89.10	$89.10	$89.10
Purchase #2	$90.56	9.442%	$99.1107	$99.11	$99.10	$99.10
Purchase #3	$25.98	3.801%	$26.9675	$26.97	$26.95	$27.00
Purchase #4	$184.50	13.566%	$209.5293	$209.53	$209.55	$209.50
Purchase #5	$191.45	6.246%	$203.408	$203.41	$203.40	$203.40
Purchase #6	$48.40	4.644%	$50.6477	$50.65	$50.65	$50.60
Purchase #7	$116.50	9.536%	$127.6094	$127.61	$127.60	$127.60
7 purchase totals =	$738.20		$806.3680	$806.38	$806.35	$806.30