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	$133.91	6.344%	$142.4053	$142.41	$142.40	$142.40
Purchase #2	$44.90	12.792%	$50.6436	$50.64	$50.65	$50.60
Purchase #3	$41.58	11.253%	$46.259	$46.26	$46.25	$46.30
Purchase #4	$174.58	5.735%	$184.5922	$184.59	$184.60	$184.60
Purchase #5	$150.75	10.638%	$166.7868	$166.79	$166.80	$166.80
Purchase #6	$230.63	12.500%	$259.4588	$259.46	$259.45	$259.50
Purchase #7	$39.34	10.237%	$43.3672	$43.37	$43.35	$43.40
7 purchase totals =	$815.69		$893.5129	$893.52	$893.50	$893.60