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	$22.69	6.344%	$24.1295	$24.13	$24.15	$24.10
Purchase #2	$196.45	5.329%	$206.9188	$206.92	$206.90	$206.90
Purchase #3	$49.40	9.170%	$53.93	$53.93	$53.95	$53.90
Purchase #4	$85.44	5.208%	$89.8897	$89.89	$89.90	$89.90
Purchase #5	$215.84	12.373%	$242.5459	$242.55	$242.55	$242.50
Purchase #6	$31.92	9.574%	$34.976	$34.98	$35.00	$35.00
Purchase #7	$152.39	12.162%	$170.9237	$170.92	$170.90	$170.90
7 purchase totals =	$754.13		$823.3136	$823.32	$823.35	$823.20