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	$16.79	11.654%	$18.7467	$18.75	$18.75	$18.70
Purchase #2	$173.64	3.674%	$180.0195	$180.02	$180.00	$180.00
Purchase #3	$186.65	5.485%	$196.8878	$196.89	$196.90	$196.90
Purchase #4	$67.72	3.783%	$70.2818	$70.28	$70.30	$70.30
Purchase #5	$72.98	3.809%	$75.7598	$75.76	$75.75	$75.80
Purchase #6	$15.99	13.304%	$18.1173	$18.12	$18.10	$18.10
Purchase #7	$93.41	13.763%	$106.266	$106.27	$106.25	$106.30
7 purchase totals =	$627.18		$666.0789	$666.09	$666.05	$666.10