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	$82.63	10.512%	$91.3161	$91.32	$91.30	$91.30
Purchase #2	$205.69	3.372%	$212.6259	$212.63	$212.65	$212.60
Purchase #3	$171.50	11.707%	$191.5775	$191.58	$191.60	$191.60
Purchase #4	$196.66	13.692%	$223.5867	$223.59	$223.60	$223.60
Purchase #5	$235.72	8.525%	$255.8151	$255.82	$255.80	$255.80
Purchase #6	$154.32	3.471%	$159.6764	$159.68	$159.70	$159.70
Purchase #7	$159.26	11.826%	$178.0941	$178.09	$178.10	$178.10
7 purchase totals =	$1,205.78		$1,312.6918	$1,312.71	$1,312.75	$1,312.70