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	$142.43	8.442%	$154.4539	$154.45	$154.45	$154.50
Purchase #2	$208.49	3.740%	$216.2875	$216.29	$216.30	$216.30
Purchase #3	$128.44	10.178%	$141.5126	$141.51	$141.50	$141.50
Purchase #4	$112.37	13.346%	$127.3669	$127.37	$127.35	$127.40
Purchase #5	$83.51	13.486%	$94.7722	$94.77	$94.75	$94.80
Purchase #6	$83.32	13.410%	$94.4932	$94.49	$94.50	$94.50
Purchase #7	$16.39	13.178%	$18.5499	$18.55	$18.55	$18.50
7 purchase totals =	$774.95		$847.4362	$847.43	$847.40	$847.50