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	$233.38	3.187%	$240.8178	$240.82	$240.80	$240.80
Purchase #2	$60.58	11.245%	$67.3922	$67.39	$67.40	$67.40
Purchase #3	$79.85	5.516%	$84.2545	$84.25	$84.25	$84.30
Purchase #4	$119.76	6.802%	$127.9061	$127.91	$127.90	$127.90
Purchase #5	$19.85	9.380%	$21.7119	$21.71	$21.70	$21.70
Purchase #6	$16.70	10.582%	$18.4672	$18.47	$18.45	$18.50
Purchase #7	$157.54	13.286%	$178.4708	$178.47	$178.45	$178.50
7 purchase totals =	$687.66		$739.0205	$739.02	$738.95	$739.10