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	$124.50	10.551%	$137.636	$137.64	$137.65	$137.60
Purchase #2	$78.80	12.847%	$88.9234	$88.92	$88.90	$88.90
Purchase #3	$35.66	6.361%	$37.9283	$37.93	$37.95	$37.90
Purchase #4	$223.58	8.612%	$242.8347	$242.83	$242.85	$242.80
Purchase #5	$143.76	6.667%	$153.3445	$153.34	$153.35	$153.30
Purchase #6	$48.93	8.196%	$52.9403	$52.94	$52.95	$52.90
Purchase #7	$167.40	11.813%	$187.175	$187.18	$187.20	$187.20
7 purchase totals =	$822.63		$900.7822	$900.78	$900.85	$900.60