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	$22.79	6.765%	$24.3317	$24.33	$24.35	$24.30
Purchase #2	$130.40	5.819%	$137.988	$137.99	$138.00	$138.00
Purchase #3	$34.45	9.262%	$37.6408	$37.64	$37.65	$37.60
Purchase #4	$127.69	13.301%	$144.674	$144.67	$144.65	$144.70
Purchase #5	$232.71	12.333%	$261.4101	$261.41	$261.40	$261.40
Purchase #6	$94.53	4.774%	$99.0429	$99.04	$99.05	$99.00
Purchase #7	$126.71	3.765%	$131.4806	$131.48	$131.50	$131.50
7 purchase totals =	$769.28		$836.5681	$836.56	$836.60	$836.50