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	$86.82	4.130%	$90.4057	$90.41	$90.40	$90.40
Purchase #2	$122.89	11.825%	$137.4217	$137.42	$137.40	$137.40
Purchase #3	$210.60	12.539%	$237.0071	$237.01	$237.00	$237.00
Purchase #4	$102.97	10.448%	$113.7283	$113.73	$113.75	$113.70
Purchase #5	$40.51	5.813%	$42.8648	$42.86	$42.85	$42.90
Purchase #6	$10.95	10.525%	$12.1025	$12.10	$12.10	$12.10
Purchase #7	$20.75	10.401%	$22.9082	$22.91	$22.90	$22.90
7 purchase totals =	$595.49		$656.4383	$656.44	$656.40	$656.40