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	$157.77	10.606%	$174.5031	$174.50	$174.50	$174.50
Purchase #2	$29.75	4.779%	$31.1718	$31.17	$31.15	$31.20
Purchase #3	$184.25	6.598%	$196.4068	$196.41	$196.40	$196.40
Purchase #4	$217.95	4.776%	$228.3593	$228.36	$228.35	$228.40
Purchase #5	$240.62	6.317%	$255.82	$255.82	$255.80	$255.80
Purchase #6	$6.78	5.653%	$7.1633	$7.16	$7.15	$7.20
Purchase #7	$99.80	3.285%	$103.0784	$103.08	$103.10	$103.10
7 purchase totals =	$936.92		$996.5027	$996.50	$996.45	$996.60