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	$36.68	10.845%	$40.6579	$40.66	$40.65	$40.70
Purchase #2	$36.50	11.387%	$40.6563	$40.66	$40.65	$40.70
Purchase #3	$134.75	5.282%	$141.8675	$141.87	$141.85	$141.90
Purchase #4	$171.82	9.823%	$188.6979	$188.70	$188.70	$188.70
Purchase #5	$66.79	6.747%	$71.2963	$71.30	$71.30	$71.30
Purchase #6	$69.59	3.582%	$72.0827	$72.08	$72.10	$72.10
Purchase #7	$225.84	12.720%	$254.5668	$254.57	$254.55	$254.60
7 purchase totals =	$741.97		$809.8254	$809.84	$809.80	$810.00