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	$28.63	9.335%	$31.3026	$31.30	$31.30	$31.30
Purchase #2	$96.38	4.654%	$100.8655	$100.87	$100.85	$100.90
Purchase #3	$142.77	11.546%	$159.2542	$159.25	$159.25	$159.30
Purchase #4	$106.70	9.150%	$116.4631	$116.46	$116.45	$116.50
Purchase #5	$42.85	6.299%	$45.5491	$45.55	$45.55	$45.50
Purchase #6	$220.42	13.134%	$249.37	$249.37	$249.35	$249.40
Purchase #7	$151.69	4.708%	$158.8316	$158.83	$158.85	$158.80
7 purchase totals =	$789.44		$861.6361	$861.63	$861.60	$861.70