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	$152.94	11.291%	$170.2085	$170.21	$170.20	$170.20
Purchase #2	$118.58	6.633%	$126.4454	$126.45	$126.45	$126.40
Purchase #3	$152.87	12.444%	$171.8931	$171.89	$171.90	$171.90
Purchase #4	$87.58	10.444%	$96.7269	$96.73	$96.75	$96.70
Purchase #5	$70.74	11.371%	$78.7838	$78.78	$78.80	$78.80
Purchase #6	$98.49	11.505%	$109.8213	$109.82	$109.80	$109.80
Purchase #7	$45.52	8.124%	$49.218	$49.22	$49.20	$49.20
7 purchase totals =	$726.72		$803.0970	$803.10	$803.10	$803.00