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	$223.97	13.320%	$253.8028	$253.80	$253.80	$253.80
Purchase #2	$112.62	9.306%	$123.1004	$123.10	$123.10	$123.10
Purchase #3	$198.68	8.457%	$215.4824	$215.48	$215.50	$215.50
Purchase #4	$95.90	7.399%	$102.9956	$103.00	$103.00	$103.00
Purchase #5	$23.31	6.806%	$24.8965	$24.90	$24.90	$24.90
Purchase #6	$127.92	7.754%	$137.8389	$137.84	$137.85	$137.80
Purchase #7	$217.68	9.711%	$238.8189	$238.82	$238.80	$238.80
7 purchase totals =	$1,000.08		$1,096.9355	$1,096.94	$1,096.95	$1,096.90