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	$64.60	9.574%	$70.7848	$70.78	$70.80	$70.80
Purchase #2	$43.38	5.281%	$45.6709	$45.67	$45.65	$45.70
Purchase #3	$153.39	11.641%	$171.2461	$171.25	$171.25	$171.20
Purchase #4	$241.90	7.622%	$260.3376	$260.34	$260.35	$260.30
Purchase #5	$196.25	13.613%	$222.9655	$222.97	$222.95	$223.00
Purchase #6	$106.89	13.648%	$121.4783	$121.48	$121.50	$121.50
Purchase #7	$172.95	13.812%	$196.8379	$196.84	$196.85	$196.80
7 purchase totals =	$979.36		$1,089.3211	$1,089.33	$1,089.35	$1,089.30