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	$47.41	6.849%	$50.6571	$50.66	$50.65	$50.70
Purchase #2	$50.37	5.711%	$53.2466	$53.25	$53.25	$53.20
Purchase #3	$13.95	3.295%	$14.4097	$14.41	$14.40	$14.40
Purchase #4	$47.61	10.861%	$52.7809	$52.78	$52.80	$52.80
Purchase #5	$89.54	11.820%	$100.1236	$100.12	$100.10	$100.10
Purchase #6	$150.98	13.780%	$171.785	$171.79	$171.80	$171.80
Purchase #7	$95.66	10.183%	$105.4011	$105.40	$105.40	$105.40
7 purchase totals =	$495.52		$548.4040	$548.41	$548.40	$548.40