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	$12.50	13.355%	$14.1694	$14.17	$14.15	$14.20
Purchase #2	$33.52	10.415%	$37.0111	$37.01	$37.00	$37.00
Purchase #3	$14.42	12.556%	$16.2306	$16.23	$16.25	$16.20
Purchase #4	$138.57	11.758%	$154.8631	$154.86	$154.85	$154.90
Purchase #5	$54.48	5.343%	$57.3909	$57.39	$57.40	$57.40
Purchase #6	$198.86	11.799%	$222.3235	$222.32	$222.30	$222.30
Purchase #7	$48.90	6.574%	$52.1147	$52.11	$52.10	$52.10
7 purchase totals =	$501.25		$554.1033	$554.09	$554.05	$554.10