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	$37.69	7.356%	$40.4625	$40.46	$40.45	$40.50
Purchase #2	$247.88	13.309%	$280.8703	$280.87	$280.85	$280.90
Purchase #3	$116.49	9.282%	$127.3026	$127.30	$127.30	$127.30
Purchase #4	$60.44	11.359%	$67.3054	$67.31	$67.30	$67.30
Purchase #5	$126.32	10.359%	$139.4055	$139.41	$139.40	$139.40
Purchase #6	$65.98	5.202%	$69.4123	$69.41	$69.40	$69.40
Purchase #7	$109.90	6.180%	$116.6918	$116.69	$116.70	$116.70
7 purchase totals =	$764.70		$841.4504	$841.45	$841.40	$841.50