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	$47.98	13.198%	$54.3124	$54.31	$54.30	$54.30
Purchase #2	$130.57	12.527%	$146.9265	$146.93	$146.95	$146.90
Purchase #3	$89.45	12.501%	$100.6321	$100.63	$100.65	$100.60
Purchase #4	$155.42	11.599%	$173.4472	$173.45	$173.45	$173.40
Purchase #5	$55.94	11.543%	$62.3972	$62.40	$62.40	$62.40
Purchase #6	$89.69	12.216%	$100.6465	$100.65	$100.65	$100.60
Purchase #7	$122.74	3.679%	$127.2556	$127.26	$127.25	$127.30
7 purchase totals =	$691.79		$765.6175	$765.63	$765.65	$765.50