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	$154.73	8.681%	$168.1621	$168.16	$168.15	$168.20
Purchase #2	$149.30	12.860%	$168.5	$168.50	$168.50	$168.50
Purchase #3	$228.71	11.606%	$255.2541	$255.25	$255.25	$255.30
Purchase #4	$101.65	7.518%	$109.292	$109.29	$109.30	$109.30
Purchase #5	$249.91	7.654%	$269.0381	$269.04	$269.05	$269.00
Purchase #6	$12.59	4.437%	$13.1486	$13.15	$13.15	$13.10
Purchase #7	$10.36	3.729%	$10.7463	$10.75	$10.75	$10.70
7 purchase totals =	$907.25		$994.1412	$994.14	$994.15	$994.10