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	$17.89	13.203%	$20.252	$20.25	$20.25	$20.30
Purchase #2	$31.31	10.762%	$34.6796	$34.68	$34.70	$34.70
Purchase #3	$39.68	8.565%	$43.0786	$43.08	$43.10	$43.10
Purchase #4	$116.27	8.715%	$126.4029	$126.40	$126.40	$126.40
Purchase #5	$31.72	8.217%	$34.3264	$34.33	$34.35	$34.30
Purchase #6	$82.87	9.515%	$90.7551	$90.76	$90.75	$90.80
Purchase #7	$73.58	9.283%	$80.4104	$80.41	$80.40	$80.40
7 purchase totals =	$393.32		$429.9050	$429.91	$429.95	$430.00