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	$141.59	12.285%	$158.9843	$158.98	$159.00	$159.00
Purchase #2	$18.62	11.528%	$20.7665	$20.77	$20.75	$20.80
Purchase #3	$119.66	3.202%	$123.4915	$123.49	$123.50	$123.50
Purchase #4	$28.43	13.219%	$32.1882	$32.19	$32.20	$32.20
Purchase #5	$36.75	8.832%	$39.9958	$40.00	$40.00	$40.00
Purchase #6	$35.50	9.286%	$38.7965	$38.80	$38.80	$38.80
Purchase #7	$208.49	6.736%	$222.5339	$222.53	$222.55	$222.50
7 purchase totals =	$589.04		$636.7567	$636.76	$636.80	$636.80