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	$130.77	11.320%	$145.5732	$145.57	$145.55	$145.60
Purchase #2	$147.30	5.123%	$154.8462	$154.85	$154.85	$154.80
Purchase #3	$226.81	10.377%	$250.3461	$250.35	$250.35	$250.30
Purchase #4	$175.49	5.680%	$185.4578	$185.46	$185.45	$185.50
Purchase #5	$17.91	10.422%	$19.7766	$19.78	$19.80	$19.80
Purchase #6	$170.37	10.132%	$187.6319	$187.63	$187.65	$187.60
Purchase #7	$69.67	3.567%	$72.1551	$72.16	$72.15	$72.20
7 purchase totals =	$938.32		$1,015.7869	$1,015.80	$1,015.80	$1,015.80