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	$35.95	12.710%	$40.5192	$40.52	$40.50	$40.50
Purchase #2	$203.42	10.659%	$225.1025	$225.10	$225.10	$225.10
Purchase #3	$131.54	4.848%	$137.9171	$137.92	$137.90	$137.90
Purchase #4	$45.78	9.114%	$49.9524	$49.95	$49.95	$50.00
Purchase #5	$72.91	11.597%	$81.3654	$81.37	$81.35	$81.40
Purchase #6	$28.40	11.546%	$31.6791	$31.68	$31.70	$31.70
Purchase #7	$92.78	6.648%	$98.948	$98.95	$98.95	$98.90
7 purchase totals =	$610.78		$665.4837	$665.49	$665.45	$665.50