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	$12.30	12.398%	$13.825	$13.83	$13.85	$13.80
Purchase #2	$181.32	5.196%	$190.7414	$190.74	$190.75	$190.70
Purchase #3	$154.28	12.642%	$173.7841	$173.78	$173.80	$173.80
Purchase #4	$150.89	3.645%	$156.3899	$156.39	$156.40	$156.40
Purchase #5	$247.80	12.526%	$278.8394	$278.84	$278.85	$278.80
Purchase #6	$195.60	7.804%	$210.8646	$210.86	$210.85	$210.90
Purchase #7	$244.77	9.554%	$268.1553	$268.16	$268.15	$268.20
7 purchase totals =	$1,186.96		$1,292.5997	$1,292.60	$1,292.65	$1,292.60