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	$96.92	4.146%	$100.9383	$100.94	$100.95	$100.90
Purchase #2	$90.75	11.207%	$100.9204	$100.92	$100.90	$100.90
Purchase #3	$40.84	10.381%	$45.0796	$45.08	$45.10	$45.10
Purchase #4	$39.55	3.259%	$40.8389	$40.84	$40.85	$40.80
Purchase #5	$236.40	4.696%	$247.5013	$247.50	$247.50	$247.50
Purchase #6	$16.92	11.536%	$18.8719	$18.87	$18.85	$18.90
Purchase #7	$108.38	5.483%	$114.3225	$114.32	$114.30	$114.30
7 purchase totals =	$629.76		$668.4729	$668.47	$668.45	$668.40