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	$170.52	11.583%	$190.2713	$190.27	$190.25	$190.30
Purchase #2	$87.36	3.400%	$90.3302	$90.33	$90.35	$90.30
Purchase #3	$140.63	10.469%	$155.3526	$155.35	$155.35	$155.40
Purchase #4	$52.48	12.481%	$59.03	$59.03	$59.05	$59.00
Purchase #5	$34.71	9.632%	$38.0533	$38.05	$38.05	$38.10
Purchase #6	$33.97	4.569%	$35.5221	$35.52	$35.50	$35.50
Purchase #7	$197.65	4.205%	$205.9612	$205.96	$205.95	$206.00
7 purchase totals =	$717.32		$774.5207	$774.51	$774.50	$774.60