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	$41.74	3.787%	$43.3207	$43.32	$43.30	$43.30
Purchase #2	$242.79	13.441%	$275.4234	$275.42	$275.40	$275.40
Purchase #3	$18.30	4.629%	$19.1471	$19.15	$19.15	$19.10
Purchase #4	$240.47	6.584%	$256.3025	$256.30	$256.30	$256.30
Purchase #5	$144.87	6.798%	$154.7183	$154.72	$154.70	$154.70
Purchase #6	$224.31	12.843%	$253.1181	$253.12	$253.10	$253.10
Purchase #7	$209.89	8.378%	$227.4746	$227.47	$227.45	$227.50
7 purchase totals =	$1,122.37		$1,229.5047	$1,229.50	$1,229.40	$1,229.40