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	$66.85	7.426%	$71.8143	$71.81	$71.80	$71.80
Purchase #2	$56.32	5.804%	$59.5888	$59.59	$59.60	$59.60
Purchase #3	$47.49	12.241%	$53.3033	$53.30	$53.30	$53.30
Purchase #4	$87.43	5.203%	$91.979	$91.98	$92.00	$92.00
Purchase #5	$16.25	3.548%	$16.8266	$16.83	$16.85	$16.80
Purchase #6	$173.65	10.329%	$191.5863	$191.59	$191.60	$191.60
Purchase #7	$140.62	11.305%	$156.5171	$156.52	$156.50	$156.50
7 purchase totals =	$588.61		$641.6154	$641.62	$641.65	$641.60