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	$48.91	11.344%	$54.4584	$54.46	$54.45	$54.50
Purchase #2	$82.32	8.194%	$89.0653	$89.07	$89.05	$89.10
Purchase #3	$120.36	10.409%	$132.8883	$132.89	$132.90	$132.90
Purchase #4	$136.66	11.547%	$152.4401	$152.44	$152.45	$152.40
Purchase #5	$126.64	3.350%	$130.8824	$130.88	$130.90	$130.90
Purchase #6	$148.28	11.127%	$164.7791	$164.78	$164.80	$164.80
Purchase #7	$35.69	8.617%	$38.7654	$38.77	$38.75	$38.80
7 purchase totals =	$698.86		$763.2790	$763.29	$763.30	$763.40