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	$14.74	5.665%	$15.575	$15.58	$15.60	$15.60
Purchase #2	$118.92	4.121%	$123.8207	$123.82	$123.80	$123.80
Purchase #3	$54.32	4.675%	$56.8595	$56.86	$56.85	$56.90
Purchase #4	$119.53	4.608%	$125.0379	$125.04	$125.05	$125.00
Purchase #5	$232.36	4.304%	$242.3608	$242.36	$242.35	$242.40
Purchase #6	$34.87	13.234%	$39.4847	$39.48	$39.50	$39.50
Purchase #7	$46.89	9.468%	$51.3295	$51.33	$51.35	$51.30
7 purchase totals =	$621.63		$654.4681	$654.47	$654.50	$654.50