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	$124.98	11.376%	$139.1977	$139.20	$139.20	$139.20
Purchase #2	$125.45	4.573%	$131.1868	$131.19	$131.20	$131.20
Purchase #3	$46.98	7.228%	$50.3757	$50.38	$50.40	$50.40
Purchase #4	$35.61	6.207%	$37.8203	$37.82	$37.80	$37.80
Purchase #5	$29.29	8.627%	$31.8168	$31.82	$31.80	$31.80
Purchase #6	$165.91	6.677%	$176.9878	$176.99	$177.00	$177.00
Purchase #7	$127.33	12.361%	$143.0693	$143.07	$143.05	$143.10
7 purchase totals =	$655.55		$710.4544	$710.47	$710.45	$710.50