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	$248.66	4.377%	$259.5438	$259.54	$259.55	$259.50
Purchase #2	$179.78	7.122%	$192.5839	$192.58	$192.60	$192.60
Purchase #3	$97.31	12.464%	$109.4387	$109.44	$109.45	$109.40
Purchase #4	$140.69	4.147%	$146.5244	$146.52	$146.50	$146.50
Purchase #5	$242.92	4.419%	$253.6546	$253.65	$253.65	$253.70
Purchase #6	$70.55	10.255%	$77.7849	$77.78	$77.80	$77.80
Purchase #7	$70.82	13.781%	$80.5797	$80.58	$80.60	$80.60
7 purchase totals =	$1,050.73		$1,120.1100	$1,120.09	$1,120.15	$1,120.10