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	$250.74	13.773%	$285.2744	$285.27	$285.25	$285.30
Purchase #2	$173.90	6.823%	$185.7652	$185.77	$185.75	$185.80
Purchase #3	$190.48	7.792%	$205.3222	$205.32	$205.30	$205.30
Purchase #4	$91.41	10.135%	$100.6744	$100.67	$100.65	$100.70
Purchase #5	$67.64	13.759%	$76.9466	$76.95	$76.95	$76.90
Purchase #6	$224.31	8.799%	$244.047	$244.05	$244.05	$244.00
Purchase #7	$52.62	12.427%	$59.1591	$59.16	$59.15	$59.20
7 purchase totals =	$1,051.10		$1,157.1889	$1,157.19	$1,157.10	$1,157.20