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	$64.50	11.354%	$71.8233	$71.82	$71.80	$71.80
Purchase #2	$59.33	5.527%	$62.6092	$62.61	$62.60	$62.60
Purchase #3	$197.82	3.811%	$205.3589	$205.36	$205.35	$205.40
Purchase #4	$162.51	9.697%	$178.2686	$178.27	$178.25	$178.30
Purchase #5	$9.92	13.620%	$11.2711	$11.27	$11.25	$11.30
Purchase #6	$214.31	5.159%	$225.3663	$225.37	$225.35	$225.40
Purchase #7	$231.32	3.208%	$238.7407	$238.74	$238.75	$238.70
7 purchase totals =	$939.71		$993.4381	$993.44	$993.35	$993.50