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	$141.67	6.216%	$150.4762	$150.48	$150.50	$150.50
Purchase #2	$121.96	9.537%	$133.5913	$133.59	$133.60	$133.60
Purchase #3	$230.28	3.660%	$238.7082	$238.71	$238.70	$238.70
Purchase #4	$115.91	7.423%	$124.514	$124.51	$124.50	$124.50
Purchase #5	$106.77	5.733%	$112.8911	$112.89	$112.90	$112.90
Purchase #6	$50.63	6.698%	$54.0212	$54.02	$54.00	$54.00
Purchase #7	$16.57	10.410%	$18.2949	$18.29	$18.30	$18.30
7 purchase totals =	$783.79		$832.4969	$832.49	$832.50	$832.50