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	$61.29	8.532%	$66.5193	$66.52	$66.50	$66.50
Purchase #2	$174.66	11.480%	$194.711	$194.71	$194.70	$194.70
Purchase #3	$184.43	4.786%	$193.2568	$193.26	$193.25	$193.30
Purchase #4	$140.57	3.524%	$145.5237	$145.52	$145.50	$145.50
Purchase #5	$55.39	13.138%	$62.6671	$62.67	$62.65	$62.70
Purchase #6	$83.52	8.779%	$90.8522	$90.85	$90.85	$90.90
Purchase #7	$61.60	6.330%	$65.4993	$65.50	$65.50	$65.50
7 purchase totals =	$761.46		$819.0294	$819.03	$818.95	$819.10