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	$150.33	4.242%	$156.707	$156.71	$156.70	$156.70
Purchase #2	$222.43	8.292%	$240.8739	$240.87	$240.85	$240.90
Purchase #3	$151.96	13.422%	$172.3561	$172.36	$172.35	$172.40
Purchase #4	$50.64	13.345%	$57.3979	$57.40	$57.40	$57.40
Purchase #5	$189.71	11.276%	$211.1017	$211.10	$211.10	$211.10
Purchase #6	$64.65	8.727%	$70.292	$70.29	$70.30	$70.30
Purchase #7	$98.42	11.683%	$109.9184	$109.92	$109.90	$109.90
7 purchase totals =	$928.14		$1,018.6470	$1,018.65	$1,018.60	$1,018.70