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	$8.34	3.298%	$8.6151	$8.62	$8.60	$8.60
Purchase #2	$89.45	9.613%	$98.0488	$98.05	$98.05	$98.00
Purchase #3	$71.37	5.651%	$75.4031	$75.40	$75.40	$75.40
Purchase #4	$127.45	13.851%	$145.1031	$145.10	$145.10	$145.10
Purchase #5	$39.93	6.643%	$42.5825	$42.58	$42.60	$42.60
Purchase #6	$98.86	10.776%	$109.5132	$109.51	$109.50	$109.50
Purchase #7	$140.49	11.154%	$156.1603	$156.16	$156.15	$156.20
7 purchase totals =	$575.89		$635.4261	$635.42	$635.40	$635.40