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	$185.87	13.729%	$211.3881	$211.39	$211.40	$211.40
Purchase #2	$53.75	6.507%	$57.2475	$57.25	$57.25	$57.20
Purchase #3	$28.40	4.168%	$29.5837	$29.58	$29.60	$29.60
Purchase #4	$22.52	12.105%	$25.246	$25.25	$25.25	$25.20
Purchase #5	$147.89	4.586%	$154.6722	$154.67	$154.65	$154.70
Purchase #6	$105.96	10.789%	$117.392	$117.39	$117.40	$117.40
Purchase #7	$77.47	10.861%	$85.884	$85.88	$85.90	$85.90
7 purchase totals =	$621.86		$681.4135	$681.41	$681.45	$681.40