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	$67.80	5.580%	$71.5832	$71.58	$71.60	$71.60
Purchase #2	$154.77	10.670%	$171.284	$171.28	$171.30	$171.30
Purchase #3	$37.83	4.111%	$39.3852	$39.39	$39.40	$39.40
Purchase #4	$75.28	10.873%	$83.4652	$83.47	$83.45	$83.50
Purchase #5	$79.61	12.192%	$89.3161	$89.32	$89.30	$89.30
Purchase #6	$172.76	9.260%	$188.7576	$188.76	$188.75	$188.80
Purchase #7	$17.78	5.211%	$18.7065	$18.71	$18.70	$18.70
7 purchase totals =	$605.83		$662.4978	$662.51	$662.50	$662.60