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	$227.49	5.559%	$240.1362	$240.14	$240.15	$240.10
Purchase #2	$238.92	10.486%	$263.9732	$263.97	$263.95	$264.00
Purchase #3	$80.61	12.820%	$90.9442	$90.94	$90.95	$90.90
Purchase #4	$100.39	11.365%	$111.7993	$111.80	$111.80	$111.80
Purchase #5	$93.92	7.298%	$100.7743	$100.77	$100.75	$100.80
Purchase #6	$247.97	8.579%	$269.2433	$269.24	$269.25	$269.20
Purchase #7	$190.41	13.259%	$215.6565	$215.66	$215.65	$215.70
7 purchase totals =	$1,179.71		$1,292.5270	$1,292.52	$1,292.50	$1,292.50