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	$79.45	5.178%	$83.5639	$83.56	$83.55	$83.60
Purchase #2	$90.81	9.571%	$99.5014	$99.50	$99.50	$99.50
Purchase #3	$231.82	3.770%	$240.5596	$240.56	$240.55	$240.60
Purchase #4	$144.60	8.721%	$157.2106	$157.21	$157.20	$157.20
Purchase #5	$152.72	6.804%	$163.1111	$163.11	$163.10	$163.10
Purchase #6	$91.90	3.301%	$94.9336	$94.93	$94.95	$94.90
Purchase #7	$56.86	4.330%	$59.322	$59.32	$59.30	$59.30
7 purchase totals =	$848.16		$898.2022	$898.19	$898.15	$898.20