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	$116.42	12.857%	$131.3881	$131.39	$131.40	$131.40
Purchase #2	$33.44	13.824%	$38.0627	$38.06	$38.05	$38.10
Purchase #3	$48.51	6.839%	$51.8276	$51.83	$51.85	$51.80
Purchase #4	$68.50	11.483%	$76.3659	$76.37	$76.35	$76.40
Purchase #5	$23.97	12.435%	$26.9507	$26.95	$26.95	$27.00
Purchase #6	$6.34	12.149%	$7.1102	$7.11	$7.10	$7.10
Purchase #7	$196.71	13.404%	$223.077	$223.08	$223.10	$223.10
7 purchase totals =	$493.89		$554.7822	$554.79	$554.80	$554.90