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	$60.94	6.718%	$65.0339	$65.03	$65.05	$65.00
Purchase #2	$180.64	7.811%	$194.7498	$194.75	$194.75	$194.70
Purchase #3	$197.67	6.155%	$209.8366	$209.84	$209.85	$209.80
Purchase #4	$152.59	3.190%	$157.4576	$157.46	$157.45	$157.50
Purchase #5	$146.58	9.355%	$160.2926	$160.29	$160.30	$160.30
Purchase #6	$80.77	13.455%	$91.6376	$91.64	$91.65	$91.60
Purchase #7	$89.51	11.567%	$99.8636	$99.86	$99.85	$99.90
7 purchase totals =	$908.70		$978.8717	$978.87	$978.90	$978.80