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	$128.60	10.662%	$142.3113	$142.31	$142.30	$142.30
Purchase #2	$50.47	6.465%	$53.7329	$53.73	$53.75	$53.70
Purchase #3	$36.64	10.518%	$40.4938	$40.49	$40.50	$40.50
Purchase #4	$103.46	11.107%	$114.9513	$114.95	$114.95	$115.00
Purchase #5	$115.29	3.833%	$119.7091	$119.71	$119.70	$119.70
Purchase #6	$99.81	6.793%	$106.5901	$106.59	$106.60	$106.60
Purchase #7	$59.80	3.309%	$61.7788	$61.78	$61.80	$61.80
7 purchase totals =	$594.07		$639.5673	$639.56	$639.60	$639.60