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	$235.39	13.623%	$267.4572	$267.46	$267.45	$267.50
Purchase #2	$150.36	10.715%	$166.4711	$166.47	$166.45	$166.50
Purchase #3	$53.48	6.190%	$56.7904	$56.79	$56.80	$56.80
Purchase #4	$30.83	8.849%	$33.5581	$33.56	$33.55	$33.60
Purchase #5	$102.99	13.326%	$116.7144	$116.71	$116.70	$116.70
Purchase #6	$81.75	10.372%	$90.2291	$90.23	$90.25	$90.20
Purchase #7	$223.61	13.378%	$253.5245	$253.52	$253.50	$253.50
7 purchase totals =	$878.41		$984.7448	$984.74	$984.70	$984.80