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	$35.82	12.129%	$40.1646	$40.16	$40.15	$40.20
Purchase #2	$37.39	7.319%	$40.1266	$40.13	$40.15	$40.10
Purchase #3	$34.29	12.392%	$38.5392	$38.54	$38.55	$38.50
Purchase #4	$54.48	12.830%	$61.4698	$61.47	$61.45	$61.50
Purchase #5	$180.35	9.454%	$197.4003	$197.40	$197.40	$197.40
Purchase #6	$196.31	8.752%	$213.4911	$213.49	$213.50	$213.50
Purchase #7	$45.39	3.145%	$46.8175	$46.82	$46.80	$46.80
7 purchase totals =	$584.03		$638.0091	$638.01	$638.00	$638.00