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	$29.93	13.282%	$33.9053	$33.91	$33.90	$33.90
Purchase #2	$67.27	4.804%	$70.5017	$70.50	$70.50	$70.50
Purchase #3	$171.26	12.451%	$192.5836	$192.58	$192.60	$192.60
Purchase #4	$79.96	3.312%	$82.6083	$82.61	$82.60	$82.60
Purchase #5	$206.27	12.326%	$231.6948	$231.69	$231.70	$231.70
Purchase #6	$98.81	12.766%	$111.4241	$111.42	$111.40	$111.40
Purchase #7	$26.76	7.521%	$28.7726	$28.77	$28.75	$28.80
7 purchase totals =	$680.26		$751.4904	$751.48	$751.45	$751.50