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	$245.30	13.855%	$279.2863	$279.29	$279.30	$279.30
Purchase #2	$56.34	12.787%	$63.5442	$63.54	$63.55	$63.50
Purchase #3	$118.76	11.707%	$132.6632	$132.66	$132.65	$132.70
Purchase #4	$18.82	8.243%	$20.3713	$20.37	$20.35	$20.40
Purchase #5	$97.25	3.567%	$100.7189	$100.72	$100.70	$100.70
Purchase #6	$92.62	13.768%	$105.3719	$105.37	$105.35	$105.40
Purchase #7	$223.51	4.840%	$234.3279	$234.33	$234.35	$234.30
7 purchase totals =	$852.60		$936.2837	$936.28	$936.25	$936.30