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	$147.81	11.763%	$165.1969	$165.20	$165.20	$165.20
Purchase #2	$46.67	6.124%	$49.5281	$49.53	$49.55	$49.50
Purchase #3	$21.48	13.243%	$24.3246	$24.32	$24.30	$24.30
Purchase #4	$172.34	12.722%	$194.2651	$194.27	$194.25	$194.30
Purchase #5	$167.61	10.816%	$185.7387	$185.74	$185.75	$185.70
Purchase #6	$116.56	10.334%	$128.6053	$128.61	$128.60	$128.60
Purchase #7	$17.92	7.593%	$19.2807	$19.28	$19.30	$19.30
7 purchase totals =	$690.39		$766.9394	$766.95	$766.95	$766.90