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	$220.76	12.775%	$248.9621	$248.96	$248.95	$249.00
Purchase #2	$57.49	6.561%	$61.2619	$61.26	$61.25	$61.30
Purchase #3	$136.59	5.196%	$143.6872	$143.69	$143.70	$143.70
Purchase #4	$141.75	13.784%	$161.2888	$161.29	$161.30	$161.30
Purchase #5	$145.45	4.150%	$151.4862	$151.49	$151.50	$151.50
Purchase #6	$69.32	4.801%	$72.6481	$72.65	$72.65	$72.60
Purchase #7	$184.72	8.473%	$200.3713	$200.37	$200.35	$200.40
7 purchase totals =	$956.08		$1,039.7056	$1,039.71	$1,039.70	$1,039.80