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	$207.71	6.514%	$221.2402	$221.24	$221.25	$221.20
Purchase #2	$137.83	13.739%	$156.7665	$156.77	$156.75	$156.80
Purchase #3	$126.57	8.309%	$137.0867	$137.09	$137.10	$137.10
Purchase #4	$152.33	9.629%	$166.9979	$167.00	$167.00	$167.00
Purchase #5	$115.83	10.231%	$127.6806	$127.68	$127.70	$127.70
Purchase #6	$98.75	9.244%	$107.8785	$107.88	$107.90	$107.90
Purchase #7	$220.87	5.673%	$233.4	$233.40	$233.40	$233.40
7 purchase totals =	$1,059.89		$1,151.0504	$1,151.06	$1,151.10	$1,151.10