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	$73.57	7.304%	$78.9436	$78.94	$78.95	$78.90
Purchase #2	$198.65	13.352%	$225.1737	$225.17	$225.15	$225.20
Purchase #3	$154.96	13.346%	$175.641	$175.64	$175.65	$175.60
Purchase #4	$234.34	13.647%	$266.3204	$266.32	$266.30	$266.30
Purchase #5	$83.64	10.718%	$92.6045	$92.60	$92.60	$92.60
Purchase #6	$17.28	13.235%	$19.567	$19.57	$19.55	$19.60
Purchase #7	$114.94	4.191%	$119.7571	$119.76	$119.75	$119.80
7 purchase totals =	$877.38		$978.0073	$978.00	$977.95	$978.00