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	$88.50	13.146%	$100.1342	$100.13	$100.15	$100.10
Purchase #2	$233.90	9.523%	$256.1743	$256.17	$256.15	$256.20
Purchase #3	$229.75	5.690%	$242.8228	$242.82	$242.80	$242.80
Purchase #4	$224.56	4.649%	$234.9998	$235.00	$235.00	$235.00
Purchase #5	$121.55	10.497%	$134.3091	$134.31	$134.30	$134.30
Purchase #6	$220.52	9.231%	$240.8762	$240.88	$240.90	$240.90
Purchase #7	$223.98	4.756%	$234.6325	$234.63	$234.65	$234.60
7 purchase totals =	$1,342.76		$1,443.9489	$1,443.94	$1,443.95	$1,443.90