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	$235.50	12.671%	$265.3402	$265.34	$265.35	$265.30
Purchase #2	$202.93	13.674%	$230.6786	$230.68	$230.70	$230.70
Purchase #3	$7.86	7.497%	$8.4493	$8.45	$8.45	$8.40
Purchase #4	$176.72	11.371%	$196.8148	$196.81	$196.80	$196.80
Purchase #5	$95.72	3.552%	$99.12	$99.12	$99.10	$99.10
Purchase #6	$142.72	11.337%	$158.9002	$158.90	$158.90	$158.90
Purchase #7	$34.73	6.722%	$37.0646	$37.06	$37.05	$37.10
7 purchase totals =	$896.18		$996.3677	$996.36	$996.35	$996.30