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	$126.44	3.219%	$130.5101	$130.51	$130.50	$130.50
Purchase #2	$82.31	7.638%	$88.5968	$88.60	$88.60	$88.60
Purchase #3	$241.38	11.214%	$268.4484	$268.45	$268.45	$268.40
Purchase #4	$47.42	7.596%	$51.022	$51.02	$51.00	$51.00
Purchase #5	$59.69	12.403%	$67.0934	$67.09	$67.10	$67.10
Purchase #6	$40.72	6.786%	$43.4833	$43.48	$43.50	$43.50
Purchase #7	$141.59	8.873%	$154.1533	$154.15	$154.15	$154.20
7 purchase totals =	$739.55		$803.3073	$803.30	$803.30	$803.30