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	$242.73	3.124%	$250.3129	$250.31	$250.30	$250.30
Purchase #2	$78.46	12.530%	$88.291	$88.29	$88.30	$88.30
Purchase #3	$81.94	10.403%	$90.4642	$90.46	$90.45	$90.50
Purchase #4	$172.97	11.715%	$193.2334	$193.23	$193.25	$193.20
Purchase #5	$8.83	13.519%	$10.0237	$10.02	$10.00	$10.00
Purchase #6	$130.98	12.730%	$147.6538	$147.65	$147.65	$147.70
Purchase #7	$149.62	11.823%	$167.3096	$167.31	$167.30	$167.30
7 purchase totals =	$865.53		$947.2886	$947.27	$947.25	$947.30