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	$45.85	6.796%	$48.966	$48.97	$48.95	$49.00
Purchase #2	$89.45	9.536%	$97.98	$97.98	$98.00	$98.00
Purchase #3	$127.96	8.715%	$139.1117	$139.11	$139.10	$139.10
Purchase #4	$216.33	4.141%	$225.2882	$225.29	$225.30	$225.30
Purchase #5	$79.52	13.686%	$90.4031	$90.40	$90.40	$90.40
Purchase #6	$106.79	10.472%	$117.973	$117.97	$117.95	$118.00
Purchase #7	$123.31	11.222%	$137.1478	$137.15	$137.15	$137.10
7 purchase totals =	$789.21		$856.8698	$856.87	$856.85	$856.90