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	$189.68	3.494%	$196.3074	$196.31	$196.30	$196.30
Purchase #2	$179.65	5.383%	$189.3206	$189.32	$189.30	$189.30
Purchase #3	$165.42	4.725%	$173.2361	$173.24	$173.25	$173.20
Purchase #4	$109.27	12.654%	$123.097	$123.10	$123.10	$123.10
Purchase #5	$122.69	9.391%	$134.2118	$134.21	$134.20	$134.20
Purchase #6	$55.96	8.622%	$60.7849	$60.78	$60.80	$60.80
Purchase #7	$88.53	13.528%	$100.5063	$100.51	$100.50	$100.50
7 purchase totals =	$911.20		$977.4641	$977.47	$977.45	$977.40