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	$171.54	4.682%	$179.5715	$179.57	$179.55	$179.60
Purchase #2	$63.45	10.338%	$70.0095	$70.01	$70.00	$70.00
Purchase #3	$106.75	4.776%	$111.8484	$111.85	$111.85	$111.80
Purchase #4	$233.92	11.727%	$261.3518	$261.35	$261.35	$261.40
Purchase #5	$249.97	6.775%	$266.9055	$266.91	$266.90	$266.90
Purchase #6	$45.46	8.115%	$49.1491	$49.15	$49.15	$49.10
Purchase #7	$42.63	5.287%	$44.8838	$44.88	$44.90	$44.90
7 purchase totals =	$913.72		$983.7196	$983.72	$983.70	$983.70