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	$115.75	11.304%	$128.8344	$128.83	$128.85	$128.80
Purchase #2	$19.27	7.536%	$20.7222	$20.72	$20.70	$20.70
Purchase #3	$113.57	9.611%	$124.4852	$124.49	$124.50	$124.50
Purchase #4	$241.27	13.730%	$274.3964	$274.40	$274.40	$274.40
Purchase #5	$69.95	3.541%	$72.4269	$72.43	$72.45	$72.40
Purchase #6	$210.44	9.696%	$230.8443	$230.84	$230.85	$230.80
Purchase #7	$132.83	13.482%	$150.7381	$150.74	$150.75	$150.70
7 purchase totals =	$903.08		$1,002.4475	$1,002.45	$1,002.50	$1,002.30