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	$200.93	9.811%	$220.6432	$220.64	$220.65	$220.60
Purchase #2	$72.70	13.537%	$82.5414	$82.54	$82.55	$82.50
Purchase #3	$99.72	8.742%	$108.4375	$108.44	$108.45	$108.40
Purchase #4	$77.49	10.863%	$85.9077	$85.91	$85.90	$85.90
Purchase #5	$80.99	11.253%	$90.1038	$90.10	$90.10	$90.10
Purchase #6	$152.52	4.796%	$159.8349	$159.83	$159.85	$159.80
Purchase #7	$181.49	4.260%	$189.2215	$189.22	$189.20	$189.20
7 purchase totals =	$865.84		$936.6900	$936.68	$936.70	$936.50