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	$10.28	8.488%	$11.1526	$11.15	$11.15	$11.20
Purchase #2	$204.57	8.654%	$222.2735	$222.27	$222.25	$222.30
Purchase #3	$222.90	8.176%	$241.1243	$241.12	$241.10	$241.10
Purchase #4	$116.61	9.196%	$127.3335	$127.33	$127.35	$127.30
Purchase #5	$31.58	5.594%	$33.3466	$33.35	$33.35	$33.30
Purchase #6	$42.85	6.774%	$45.7527	$45.75	$45.75	$45.80
Purchase #7	$150.68	13.644%	$171.2388	$171.24	$171.25	$171.20
7 purchase totals =	$779.47		$852.2220	$852.21	$852.20	$852.20