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	$75.84	13.280%	$85.9116	$85.91	$85.90	$85.90
Purchase #2	$146.95	11.719%	$164.1711	$164.17	$164.15	$164.20
Purchase #3	$43.72	11.665%	$48.8199	$48.82	$48.80	$48.80
Purchase #4	$73.29	9.743%	$80.4306	$80.43	$80.45	$80.40
Purchase #5	$115.29	10.559%	$127.4635	$127.46	$127.45	$127.50
Purchase #6	$227.74	4.675%	$238.3868	$238.39	$238.40	$238.40
Purchase #7	$196.98	4.552%	$205.9465	$205.95	$205.95	$205.90
7 purchase totals =	$879.81		$951.1300	$951.13	$951.10	$951.10