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	$9.49	11.253%	$10.5579	$10.56	$10.55	$10.60
Purchase #2	$29.87	13.503%	$33.9033	$33.90	$33.90	$33.90
Purchase #3	$42.74	9.603%	$46.8443	$46.84	$46.85	$46.80
Purchase #4	$75.97	12.385%	$85.3789	$85.38	$85.40	$85.40
Purchase #5	$59.29	4.178%	$61.7671	$61.77	$61.75	$61.80
Purchase #6	$31.27	12.494%	$35.1769	$35.18	$35.20	$35.20
Purchase #7	$235.59	4.144%	$245.3528	$245.35	$245.35	$245.40
7 purchase totals =	$484.22		$518.9812	$518.98	$519.00	$519.10