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	$97.80	7.790%	$105.4186	$105.42	$105.40	$105.40
Purchase #2	$221.86	10.693%	$245.5835	$245.58	$245.60	$245.60
Purchase #3	$134.55	5.226%	$141.5816	$141.58	$141.60	$141.60
Purchase #4	$223.89	4.126%	$233.1277	$233.13	$233.15	$233.10
Purchase #5	$30.75	9.505%	$33.6728	$33.67	$33.65	$33.70
Purchase #6	$29.73	13.483%	$33.7385	$33.74	$33.75	$33.70
Purchase #7	$109.69	10.865%	$121.6078	$121.61	$121.60	$121.60
7 purchase totals =	$848.27		$914.7305	$914.73	$914.75	$914.70