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	$16.67	11.833%	$18.6426	$18.64	$18.65	$18.60
Purchase #2	$44.95	9.850%	$49.3776	$49.38	$49.40	$49.40
Purchase #3	$112.46	13.688%	$127.8535	$127.85	$127.85	$127.90
Purchase #4	$117.56	7.608%	$126.504	$126.50	$126.50	$126.50
Purchase #5	$20.41	13.466%	$23.1584	$23.16	$23.15	$23.20
Purchase #6	$45.41	7.665%	$48.8907	$48.89	$48.90	$48.90
Purchase #7	$134.91	4.473%	$140.9445	$140.94	$140.95	$140.90
7 purchase totals =	$492.37		$535.3713	$535.36	$535.40	$535.40