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	$64.92	10.775%	$71.9151	$71.92	$71.90	$71.90
Purchase #2	$189.47	8.689%	$205.933	$205.93	$205.95	$205.90
Purchase #3	$59.65	5.403%	$62.8729	$62.87	$62.85	$62.90
Purchase #4	$215.86	13.476%	$244.9493	$244.95	$244.95	$244.90
Purchase #5	$27.38	4.513%	$28.6157	$28.62	$28.60	$28.60
Purchase #6	$61.95	5.809%	$65.5487	$65.55	$65.55	$65.50
Purchase #7	$142.66	11.518%	$159.0916	$159.09	$159.10	$159.10
7 purchase totals =	$761.89		$838.9263	$838.93	$838.90	$838.80