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	$157.52	3.729%	$163.3939	$163.39	$163.40	$163.40
Purchase #2	$71.64	7.388%	$76.9328	$76.93	$76.95	$76.90
Purchase #3	$85.69	4.471%	$89.5212	$89.52	$89.50	$89.50
Purchase #4	$152.51	10.276%	$168.1819	$168.18	$168.20	$168.20
Purchase #5	$18.90	11.140%	$21.0055	$21.01	$21.00	$21.00
Purchase #6	$175.81	5.306%	$185.1385	$185.14	$185.15	$185.10
Purchase #7	$206.79	9.859%	$227.1774	$227.18	$227.20	$227.20
7 purchase totals =	$868.86		$931.3512	$931.35	$931.40	$931.30