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	$79.55	12.529%	$89.5168	$89.52	$89.50	$89.50
Purchase #2	$99.86	11.746%	$111.5896	$111.59	$111.60	$111.60
Purchase #3	$42.91	10.161%	$47.2701	$47.27	$47.25	$47.30
Purchase #4	$235.27	10.511%	$259.9992	$260.00	$260.00	$260.00
Purchase #5	$210.85	3.238%	$217.6773	$217.68	$217.70	$217.70
Purchase #6	$236.75	7.173%	$253.7321	$253.73	$253.75	$253.70
Purchase #7	$198.68	5.435%	$209.4783	$209.48	$209.50	$209.50
7 purchase totals =	$1,103.87		$1,189.2634	$1,189.27	$1,189.30	$1,189.30