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	$47.68	12.124%	$53.4607	$53.46	$53.45	$53.50
Purchase #2	$210.82	10.674%	$233.3229	$233.32	$233.30	$233.30
Purchase #3	$57.86	10.711%	$64.0574	$64.06	$64.05	$64.10
Purchase #4	$15.39	5.819%	$16.2855	$16.29	$16.30	$16.30
Purchase #5	$234.51	11.265%	$260.9276	$260.93	$260.95	$260.90
Purchase #6	$24.42	4.247%	$25.4571	$25.46	$25.45	$25.50
Purchase #7	$12.67	12.381%	$14.2387	$14.24	$14.25	$14.20
7 purchase totals =	$603.35		$667.7499	$667.76	$667.75	$667.80