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	$85.62	6.124%	$90.8634	$90.86	$90.85	$90.90
Purchase #2	$116.48	6.335%	$123.859	$123.86	$123.85	$123.90
Purchase #3	$156.52	10.727%	$173.3099	$173.31	$173.30	$173.30
Purchase #4	$83.75	8.135%	$90.5631	$90.56	$90.55	$90.60
Purchase #5	$77.47	10.669%	$85.7353	$85.74	$85.75	$85.70
Purchase #6	$64.35	6.642%	$68.6241	$68.62	$68.60	$68.60
Purchase #7	$173.49	8.591%	$188.3945	$188.39	$188.40	$188.40
7 purchase totals =	$757.68		$821.3493	$821.34	$821.30	$821.40