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	$28.32	7.680%	$30.495	$30.50	$30.50	$30.50
Purchase #2	$180.31	12.839%	$203.46	$203.46	$203.45	$203.50
Purchase #3	$70.90	10.223%	$78.1481	$78.15	$78.15	$78.10
Purchase #4	$34.71	11.852%	$38.8238	$38.82	$38.80	$38.80
Purchase #5	$68.78	13.169%	$77.8376	$77.84	$77.85	$77.80
Purchase #6	$73.97	10.639%	$81.8397	$81.84	$81.85	$81.80
Purchase #7	$208.39	10.152%	$229.5458	$229.55	$229.55	$229.50
7 purchase totals =	$665.38		$740.1500	$740.16	$740.15	$740.00