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	$55.98	4.160%	$58.3088	$58.31	$58.30	$58.30
Purchase #2	$106.48	11.657%	$118.8924	$118.89	$118.90	$118.90
Purchase #3	$83.92	7.738%	$90.4137	$90.41	$90.40	$90.40
Purchase #4	$48.27	7.331%	$51.8087	$51.81	$51.80	$51.80
Purchase #5	$51.38	11.126%	$57.0965	$57.10	$57.10	$57.10
Purchase #6	$152.92	12.781%	$172.4647	$172.46	$172.45	$172.50
Purchase #7	$49.26	12.456%	$55.3958	$55.40	$55.40	$55.40
7 purchase totals =	$548.21		$604.3806	$604.38	$604.35	$604.40