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	$71.71	3.410%	$74.1553	$74.16	$74.15	$74.20
Purchase #2	$141.75	10.703%	$156.9215	$156.92	$156.90	$156.90
Purchase #3	$79.95	12.626%	$90.0445	$90.04	$90.05	$90.00
Purchase #4	$200.27	8.187%	$216.6661	$216.67	$216.65	$216.70
Purchase #5	$204.99	8.552%	$222.5207	$222.52	$222.50	$222.50
Purchase #6	$30.38	9.657%	$33.3138	$33.31	$33.30	$33.30
Purchase #7	$9.38	12.608%	$10.5626	$10.56	$10.55	$10.60
7 purchase totals =	$738.43		$804.1845	$804.18	$804.10	$804.20