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	$72.57	13.634%	$82.4642	$82.46	$82.45	$82.50
Purchase #2	$33.49	10.803%	$37.1079	$37.11	$37.10	$37.10
Purchase #3	$144.72	11.375%	$161.1819	$161.18	$161.20	$161.20
Purchase #4	$193.39	6.364%	$205.6973	$205.70	$205.70	$205.70
Purchase #5	$71.72	12.371%	$80.5925	$80.59	$80.60	$80.60
Purchase #6	$150.86	7.452%	$162.1021	$162.10	$162.10	$162.10
Purchase #7	$132.89	11.659%	$148.3836	$148.38	$148.40	$148.40
7 purchase totals =	$799.64		$877.5295	$877.52	$877.55	$877.60