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	$166.39	12.583%	$187.3269	$187.33	$187.35	$187.30
Purchase #2	$197.47	8.489%	$214.2332	$214.23	$214.25	$214.20
Purchase #3	$52.99	3.620%	$54.9082	$54.91	$54.90	$54.90
Purchase #4	$59.44	12.231%	$66.7101	$66.71	$66.70	$66.70
Purchase #5	$55.76	10.700%	$61.7263	$61.73	$61.75	$61.70
Purchase #6	$40.92	7.107%	$43.8282	$43.83	$43.85	$43.80
Purchase #7	$240.26	4.443%	$250.9348	$250.93	$250.95	$250.90
7 purchase totals =	$813.23		$879.6677	$879.67	$879.75	$879.50