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	$38.37	12.508%	$43.1693	$43.17	$43.15	$43.20
Purchase #2	$119.79	7.580%	$128.8701	$128.87	$128.85	$128.90
Purchase #3	$93.66	12.744%	$105.596	$105.60	$105.60	$105.60
Purchase #4	$129.57	13.631%	$147.2317	$147.23	$147.25	$147.20
Purchase #5	$135.89	6.750%	$145.0626	$145.06	$145.05	$145.10
Purchase #6	$250.48	9.277%	$273.717	$273.72	$273.70	$273.70
Purchase #7	$228.98	5.429%	$241.4113	$241.41	$241.40	$241.40
7 purchase totals =	$996.74		$1,085.0580	$1,085.06	$1,085.00	$1,085.10