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	$31.77	7.571%	$34.1753	$34.18	$34.20	$34.20
Purchase #2	$114.48	10.436%	$126.4271	$126.43	$126.45	$126.40
Purchase #3	$46.27	13.608%	$52.5664	$52.57	$52.55	$52.60
Purchase #4	$187.42	11.129%	$208.278	$208.28	$208.30	$208.30
Purchase #5	$47.84	11.298%	$53.245	$53.25	$53.25	$53.20
Purchase #6	$90.38	10.367%	$99.7497	$99.75	$99.75	$99.70
Purchase #7	$39.91	6.262%	$42.4092	$42.41	$42.40	$42.40
7 purchase totals =	$558.07		$616.8507	$616.87	$616.90	$616.80