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	$29.73	10.640%	$32.8933	$32.89	$32.90	$32.90
Purchase #2	$114.62	7.638%	$123.3747	$123.37	$123.35	$123.40
Purchase #3	$60.50	8.500%	$65.6425	$65.64	$65.65	$65.60
Purchase #4	$242.62	11.846%	$271.3608	$271.36	$271.35	$271.40
Purchase #5	$102.53	10.382%	$113.1747	$113.17	$113.15	$113.20
Purchase #6	$176.78	8.523%	$191.847	$191.85	$191.85	$191.80
Purchase #7	$40.58	3.575%	$42.0307	$42.03	$42.05	$42.00
7 purchase totals =	$767.36		$840.3237	$840.31	$840.30	$840.30