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	$60.44	10.141%	$66.5692	$66.57	$66.55	$66.60
Purchase #2	$191.25	6.660%	$203.9873	$203.99	$204.00	$204.00
Purchase #3	$104.89	10.203%	$115.5919	$115.59	$115.60	$115.60
Purchase #4	$203.54	9.353%	$222.5771	$222.58	$222.60	$222.60
Purchase #5	$19.63	6.181%	$20.8433	$20.84	$20.85	$20.80
Purchase #6	$113.73	8.584%	$123.4926	$123.49	$123.50	$123.50
Purchase #7	$53.59	6.830%	$57.2502	$57.25	$57.25	$57.30
7 purchase totals =	$747.07		$810.3116	$810.31	$810.35	$810.40