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	$80.39	11.596%	$89.712	$89.71	$89.70	$89.70
Purchase #2	$47.68	12.435%	$53.609	$53.61	$53.60	$53.60
Purchase #3	$191.56	13.644%	$217.6964	$217.70	$217.70	$217.70
Purchase #4	$219.38	4.181%	$228.5523	$228.55	$228.55	$228.60
Purchase #5	$53.51	8.634%	$58.1301	$58.13	$58.15	$58.10
Purchase #6	$87.73	11.219%	$97.5724	$97.57	$97.55	$97.60
Purchase #7	$92.79	7.208%	$99.4783	$99.48	$99.50	$99.50
7 purchase totals =	$773.04		$844.7505	$844.75	$844.75	$844.80