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	$233.49	13.181%	$264.2663	$264.27	$264.25	$264.30
Purchase #2	$109.66	7.770%	$118.1806	$118.18	$118.20	$118.20
Purchase #3	$233.91	11.510%	$260.833	$260.83	$260.85	$260.80
Purchase #4	$21.73	8.555%	$23.589	$23.59	$23.60	$23.60
Purchase #5	$105.48	3.413%	$109.08	$109.08	$109.10	$109.10
Purchase #6	$144.40	6.452%	$153.7167	$153.72	$153.70	$153.70
Purchase #7	$88.88	13.541%	$100.9152	$100.92	$100.90	$100.90
7 purchase totals =	$937.55		$1,030.5808	$1,030.59	$1,030.60	$1,030.60