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	$166.57	11.366%	$185.5023	$185.50	$185.50	$185.50
Purchase #2	$85.68	7.136%	$91.7941	$91.79	$91.80	$91.80
Purchase #3	$46.41	11.730%	$51.8539	$51.85	$51.85	$51.90
Purchase #4	$53.66	11.643%	$59.9076	$59.91	$59.90	$59.90
Purchase #5	$99.89	8.460%	$108.3407	$108.34	$108.35	$108.30
Purchase #6	$12.40	7.207%	$13.2937	$13.29	$13.30	$13.30
Purchase #7	$69.68	6.519%	$74.2224	$74.22	$74.20	$74.20
7 purchase totals =	$534.29		$584.9147	$584.90	$584.90	$584.90