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	$130.80	13.143%	$147.991	$147.99	$148.00	$148.00
Purchase #2	$96.54	13.737%	$109.8017	$109.80	$109.80	$109.80
Purchase #3	$160.86	7.865%	$173.5116	$173.51	$173.50	$173.50
Purchase #4	$237.92	7.791%	$256.4563	$256.46	$256.45	$256.50
Purchase #5	$166.80	3.363%	$172.4095	$172.41	$172.40	$172.40
Purchase #6	$245.34	12.869%	$276.9128	$276.91	$276.90	$276.90
Purchase #7	$146.84	13.617%	$166.8352	$166.84	$166.85	$166.80
7 purchase totals =	$1,185.10		$1,303.9181	$1,303.92	$1,303.90	$1,303.90