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	$218.83	13.298%	$247.93	$247.93	$247.95	$247.90
Purchase #2	$228.95	10.764%	$253.5942	$253.59	$253.60	$253.60
Purchase #3	$37.98	13.819%	$43.2285	$43.23	$43.25	$43.20
Purchase #4	$99.72	12.215%	$111.9008	$111.90	$111.90	$111.90
Purchase #5	$203.72	4.116%	$212.1051	$212.11	$212.10	$212.10
Purchase #6	$210.61	9.336%	$230.2725	$230.27	$230.25	$230.30
Purchase #7	$41.99	7.234%	$45.0276	$45.03	$45.05	$45.00
7 purchase totals =	$1,041.80		$1,144.0587	$1,144.06	$1,144.10	$1,144.00