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	$201.31	10.637%	$222.7233	$222.72	$222.70	$222.70
Purchase #2	$173.84	11.868%	$194.4713	$194.47	$194.45	$194.50
Purchase #3	$125.96	9.146%	$137.4803	$137.48	$137.50	$137.50
Purchase #4	$96.86	3.854%	$100.593	$100.59	$100.60	$100.60
Purchase #5	$127.77	13.589%	$145.1327	$145.13	$145.15	$145.10
Purchase #6	$61.49	8.791%	$66.8956	$66.90	$66.90	$66.90
Purchase #7	$105.31	4.376%	$109.9184	$109.92	$109.90	$109.90
7 purchase totals =	$892.54		$977.2146	$977.21	$977.20	$977.20