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	$205.34	3.599%	$212.7302	$212.73	$212.75	$212.70
Purchase #2	$225.37	11.615%	$251.5467	$251.55	$251.55	$251.50
Purchase #3	$119.53	3.760%	$124.0243	$124.02	$124.00	$124.00
Purchase #4	$74.27	5.572%	$78.4083	$78.41	$78.40	$78.40
Purchase #5	$90.67	13.647%	$103.0437	$103.04	$103.05	$103.00
Purchase #6	$43.66	10.568%	$48.274	$48.27	$48.25	$48.30
Purchase #7	$151.34	7.281%	$162.3591	$162.36	$162.35	$162.40
7 purchase totals =	$910.18		$980.3863	$980.38	$980.35	$980.30