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	$25.69	13.142%	$29.0662	$29.07	$29.05	$29.10
Purchase #2	$34.86	7.650%	$37.5268	$37.53	$37.55	$37.50
Purchase #3	$223.93	8.127%	$242.1288	$242.13	$242.15	$242.10
Purchase #4	$105.41	7.113%	$112.9078	$112.91	$112.90	$112.90
Purchase #5	$125.61	6.756%	$134.0962	$134.10	$134.10	$134.10
Purchase #6	$17.72	4.234%	$18.4703	$18.47	$18.45	$18.50
Purchase #7	$141.42	13.788%	$160.919	$160.92	$160.90	$160.90
7 purchase totals =	$674.64		$735.1151	$735.13	$735.10	$735.10