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	$249.77	5.688%	$263.9769	$263.98	$264.00	$264.00
Purchase #2	$109.84	13.447%	$124.6102	$124.61	$124.60	$124.60
Purchase #3	$221.61	13.678%	$251.9218	$251.92	$251.90	$251.90
Purchase #4	$8.82	6.610%	$9.403	$9.40	$9.40	$9.40
Purchase #5	$238.25	9.226%	$260.2309	$260.23	$260.25	$260.20
Purchase #6	$41.72	4.484%	$43.5907	$43.59	$43.60	$43.60
Purchase #7	$43.41	13.237%	$49.1562	$49.16	$49.15	$49.20
7 purchase totals =	$913.42		$1,002.8897	$1,002.89	$1,002.90	$1,002.90