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	$206.64	4.305%	$215.5359	$215.54	$215.55	$215.50
Purchase #2	$154.56	10.105%	$170.1783	$170.18	$170.20	$170.20
Purchase #3	$207.37	10.110%	$228.3351	$228.34	$228.35	$228.30
Purchase #4	$247.63	4.377%	$258.4688	$258.47	$258.45	$258.50
Purchase #5	$127.86	3.668%	$132.5499	$132.55	$132.55	$132.50
Purchase #6	$91.89	12.325%	$103.2154	$103.22	$103.20	$103.20
Purchase #7	$142.78	12.481%	$160.6004	$160.60	$160.60	$160.60
7 purchase totals =	$1,178.73		$1,268.8838	$1,268.90	$1,268.90	$1,268.80