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	$47.27	9.177%	$51.608	$51.61	$51.60	$51.60
Purchase #2	$105.75	10.405%	$116.7533	$116.75	$116.75	$116.80
Purchase #3	$179.99	11.349%	$200.4171	$200.42	$200.40	$200.40
Purchase #4	$210.39	13.223%	$238.2099	$238.21	$238.20	$238.20
Purchase #5	$40.63	12.388%	$45.6632	$45.66	$45.65	$45.70
Purchase #6	$126.28	11.119%	$140.3211	$140.32	$140.30	$140.30
Purchase #7	$60.46	11.538%	$67.4359	$67.44	$67.45	$67.40
7 purchase totals =	$770.77		$860.4085	$860.41	$860.35	$860.40