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	$165.91	12.740%	$187.0469	$187.05	$187.05	$187.00
Purchase #2	$40.50	8.104%	$43.7821	$43.78	$43.80	$43.80
Purchase #3	$192.86	11.784%	$215.5866	$215.59	$215.60	$215.60
Purchase #4	$242.76	3.428%	$251.0818	$251.08	$251.10	$251.10
Purchase #5	$226.49	5.589%	$239.1485	$239.15	$239.15	$239.10
Purchase #6	$179.47	6.513%	$191.1589	$191.16	$191.15	$191.20
Purchase #7	$83.70	12.820%	$94.4303	$94.43	$94.45	$94.40
7 purchase totals =	$1,131.69		$1,222.2351	$1,222.24	$1,222.30	$1,222.20