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	$240.89	12.142%	$270.1389	$270.14	$270.15	$270.10
Purchase #2	$12.82	3.792%	$13.3061	$13.31	$13.30	$13.30
Purchase #3	$41.69	10.322%	$45.9932	$45.99	$46.00	$46.00
Purchase #4	$105.64	5.285%	$111.2231	$111.22	$111.20	$111.20
Purchase #5	$84.71	11.675%	$94.5999	$94.60	$94.60	$94.60
Purchase #6	$244.76	10.538%	$270.5528	$270.55	$270.55	$270.60
Purchase #7	$131.44	12.854%	$148.3353	$148.34	$148.35	$148.30
7 purchase totals =	$861.95		$954.1493	$954.15	$954.15	$954.10