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	$205.73	6.694%	$219.5016	$219.50	$219.50	$219.50
Purchase #2	$34.56	10.796%	$38.2911	$38.29	$38.30	$38.30
Purchase #3	$91.46	11.289%	$101.7849	$101.78	$101.80	$101.80
Purchase #4	$176.38	8.484%	$191.3441	$191.34	$191.35	$191.30
Purchase #5	$48.51	4.223%	$50.5586	$50.56	$50.55	$50.60
Purchase #6	$88.84	13.249%	$100.6104	$100.61	$100.60	$100.60
Purchase #7	$195.91	11.784%	$218.996	$219.00	$219.00	$219.00
7 purchase totals =	$841.39		$921.0867	$921.08	$921.10	$921.10