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	$115.82	6.306%	$123.1236	$123.12	$123.10	$123.10
Purchase #2	$48.88	7.445%	$52.5191	$52.52	$52.50	$52.50
Purchase #3	$138.26	13.248%	$156.5767	$156.58	$156.60	$156.60
Purchase #4	$67.33	7.688%	$72.5063	$72.51	$72.50	$72.50
Purchase #5	$113.40	5.505%	$119.6427	$119.64	$119.65	$119.60
Purchase #6	$46.87	8.325%	$50.7719	$50.77	$50.75	$50.80
Purchase #7	$193.77	8.335%	$209.9207	$209.92	$209.90	$209.90
7 purchase totals =	$724.33		$785.0610	$785.06	$785.00	$785.00