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	$139.48	6.762%	$148.9116	$148.91	$148.90	$148.90
Purchase #2	$164.83	10.589%	$182.2838	$182.28	$182.30	$182.30
Purchase #3	$233.46	6.396%	$248.3921	$248.39	$248.40	$248.40
Purchase #4	$126.46	11.134%	$140.5401	$140.54	$140.55	$140.50
Purchase #5	$79.30	11.387%	$88.3299	$88.33	$88.35	$88.30
Purchase #6	$62.81	12.714%	$70.7957	$70.80	$70.80	$70.80
Purchase #7	$56.48	8.182%	$61.1012	$61.10	$61.10	$61.10
7 purchase totals =	$862.82		$940.3544	$940.35	$940.40	$940.30