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	$209.47	4.499%	$218.8941	$218.89	$218.90	$218.90
Purchase #2	$116.74	7.867%	$125.9239	$125.92	$125.90	$125.90
Purchase #3	$48.39	4.518%	$50.5763	$50.58	$50.60	$50.60
Purchase #4	$132.70	13.123%	$150.1142	$150.11	$150.10	$150.10
Purchase #5	$63.35	9.341%	$69.2675	$69.27	$69.25	$69.30
Purchase #6	$141.83	11.721%	$158.4539	$158.45	$158.45	$158.50
Purchase #7	$63.49	13.434%	$72.0192	$72.02	$72.00	$72.00
7 purchase totals =	$775.97		$845.2491	$845.24	$845.20	$845.30