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	$52.61	13.631%	$59.7813	$59.78	$59.80	$59.80
Purchase #2	$197.91	3.467%	$204.7715	$204.77	$204.75	$204.80
Purchase #3	$224.71	11.252%	$249.9944	$249.99	$250.00	$250.00
Purchase #4	$138.57	11.316%	$154.2506	$154.25	$154.25	$154.30
Purchase #5	$61.90	13.115%	$70.0182	$70.02	$70.00	$70.00
Purchase #6	$53.92	10.321%	$59.4851	$59.49	$59.50	$59.50
Purchase #7	$159.39	3.817%	$165.4739	$165.47	$165.45	$165.50
7 purchase totals =	$889.01		$963.7750	$963.77	$963.75	$963.90