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	$124.87	5.125%	$131.2696	$131.27	$131.25	$131.30
Purchase #2	$84.74	11.159%	$94.1961	$94.20	$94.20	$94.20
Purchase #3	$93.40	13.855%	$106.3406	$106.34	$106.35	$106.30
Purchase #4	$83.32	3.670%	$86.3778	$86.38	$86.40	$86.40
Purchase #5	$239.75	5.640%	$253.2719	$253.27	$253.25	$253.30
Purchase #6	$39.54	7.327%	$42.4371	$42.44	$42.45	$42.40
Purchase #7	$188.60	4.378%	$196.8569	$196.86	$196.85	$196.90
7 purchase totals =	$854.22		$910.7500	$910.76	$910.75	$910.80