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	$142.87	11.651%	$159.5158	$159.52	$159.50	$159.50
Purchase #2	$148.83	3.310%	$153.7563	$153.76	$153.75	$153.80
Purchase #3	$64.52	9.781%	$70.8307	$70.83	$70.85	$70.80
Purchase #4	$225.78	5.339%	$237.8344	$237.83	$237.85	$237.80
Purchase #5	$106.61	9.673%	$116.9224	$116.92	$116.90	$116.90
Purchase #6	$30.74	8.392%	$33.3197	$33.32	$33.30	$33.30
Purchase #7	$242.78	13.392%	$275.2931	$275.29	$275.30	$275.30
7 purchase totals =	$962.13		$1,047.4724	$1,047.47	$1,047.45	$1,047.40