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	$78.89	13.127%	$89.2459	$89.25	$89.25	$89.20
Purchase #2	$84.75	6.749%	$90.4698	$90.47	$90.45	$90.50
Purchase #3	$209.36	4.779%	$219.3653	$219.37	$219.35	$219.40
Purchase #4	$102.45	7.688%	$110.3264	$110.33	$110.35	$110.30
Purchase #5	$16.69	6.209%	$17.7263	$17.73	$17.75	$17.70
Purchase #6	$109.41	7.397%	$117.5031	$117.50	$117.50	$117.50
Purchase #7	$34.27	13.595%	$38.929	$38.93	$38.95	$38.90
7 purchase totals =	$635.82		$683.5658	$683.58	$683.60	$683.50