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	$123.83	11.215%	$137.7175	$137.72	$137.70	$137.70
Purchase #2	$31.53	5.424%	$33.2402	$33.24	$33.25	$33.20
Purchase #3	$49.74	13.866%	$56.6369	$56.64	$56.65	$56.60
Purchase #4	$17.71	4.843%	$18.5677	$18.57	$18.55	$18.60
Purchase #5	$249.94	13.811%	$284.4592	$284.46	$284.45	$284.50
Purchase #6	$55.64	7.356%	$59.7329	$59.73	$59.75	$59.70
Purchase #7	$229.61	11.733%	$256.5501	$256.55	$256.55	$256.60
7 purchase totals =	$758.00		$846.9045	$846.91	$846.90	$846.90