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	$29.36	8.844%	$31.9566	$31.96	$31.95	$32.00
Purchase #2	$77.50	4.417%	$80.9232	$80.92	$80.90	$80.90
Purchase #3	$39.78	8.584%	$43.1947	$43.19	$43.20	$43.20
Purchase #4	$88.51	11.378%	$98.5807	$98.58	$98.60	$98.60
Purchase #5	$180.40	5.359%	$190.0676	$190.07	$190.05	$190.10
Purchase #6	$158.54	5.325%	$166.9823	$166.98	$167.00	$167.00
Purchase #7	$56.76	5.282%	$59.7581	$59.76	$59.75	$59.80
7 purchase totals =	$630.85		$671.4632	$671.46	$671.45	$671.60