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	$159.89	5.640%	$168.9078	$168.91	$168.90	$168.90
Purchase #2	$21.52	13.809%	$24.4917	$24.49	$24.50	$24.50
Purchase #3	$120.86	5.729%	$127.7841	$127.78	$127.80	$127.80
Purchase #4	$115.54	6.253%	$122.7647	$122.76	$122.75	$122.80
Purchase #5	$24.96	13.745%	$28.3908	$28.39	$28.40	$28.40
Purchase #6	$137.91	9.822%	$151.4555	$151.46	$151.45	$151.50
Purchase #7	$240.70	9.106%	$262.6181	$262.62	$262.60	$262.60
7 purchase totals =	$821.38		$886.4127	$886.41	$886.40	$886.50