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	$166.84	11.772%	$186.4804	$186.48	$186.50	$186.50
Purchase #2	$49.99	13.675%	$56.8261	$56.83	$56.85	$56.80
Purchase #3	$69.37	3.620%	$71.8812	$71.88	$71.90	$71.90
Purchase #4	$134.85	10.365%	$148.8272	$148.83	$148.85	$148.80
Purchase #5	$53.95	8.360%	$58.4602	$58.46	$58.45	$58.50
Purchase #6	$42.45	11.862%	$47.4854	$47.49	$47.50	$47.50
Purchase #7	$49.70	3.291%	$51.3356	$51.34	$51.35	$51.30
7 purchase totals =	$567.15		$621.2961	$621.31	$621.40	$621.30