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	$15.80	10.234%	$17.417	$17.42	$17.40	$17.40
Purchase #2	$156.47	7.421%	$168.0816	$168.08	$168.10	$168.10
Purchase #3	$146.85	3.140%	$151.4611	$151.46	$151.45	$151.50
Purchase #4	$179.86	6.361%	$191.3009	$191.30	$191.30	$191.30
Purchase #5	$56.63	4.667%	$59.2729	$59.27	$59.25	$59.30
Purchase #6	$158.98	3.271%	$164.1802	$164.18	$164.20	$164.20
Purchase #7	$171.99	11.540%	$191.8376	$191.84	$191.85	$191.80
7 purchase totals =	$886.58		$943.5513	$943.55	$943.55	$943.60