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	$26.36	8.709%	$28.6557	$28.66	$28.65	$28.70
Purchase #2	$36.60	4.857%	$38.3777	$38.38	$38.40	$38.40
Purchase #3	$111.90	11.624%	$124.9073	$124.91	$124.90	$124.90
Purchase #4	$32.97	12.623%	$37.1318	$37.13	$37.15	$37.10
Purchase #5	$157.55	3.131%	$162.4829	$162.48	$162.50	$162.50
Purchase #6	$28.35	7.537%	$30.4867	$30.49	$30.50	$30.50
Purchase #7	$76.61	8.343%	$83.0016	$83.00	$83.00	$83.00
7 purchase totals =	$470.34		$505.0437	$505.05	$505.10	$505.10