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	$147.92	5.559%	$156.1429	$156.14	$156.15	$156.10
Purchase #2	$107.78	3.785%	$111.8595	$111.86	$111.85	$111.90
Purchase #3	$122.64	7.267%	$131.5522	$131.55	$131.55	$131.60
Purchase #4	$32.25	9.611%	$35.3495	$35.35	$35.35	$35.30
Purchase #5	$112.59	12.659%	$126.8428	$126.84	$126.85	$126.80
Purchase #6	$10.92	4.415%	$11.4021	$11.40	$11.40	$11.40
Purchase #7	$85.95	9.720%	$94.3043	$94.30	$94.30	$94.30
7 purchase totals =	$620.05		$667.4533	$667.44	$667.45	$667.40