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	$156.72	5.776%	$165.7721	$165.77	$165.75	$165.80
Purchase #2	$47.75	7.399%	$51.283	$51.28	$51.30	$51.30
Purchase #3	$72.95	6.241%	$77.5028	$77.50	$77.50	$77.50
Purchase #4	$64.56	4.523%	$67.48	$67.48	$67.50	$67.50
Purchase #5	$95.95	4.218%	$99.9972	$100.00	$100.00	$100.00
Purchase #6	$89.57	5.615%	$94.5994	$94.60	$94.60	$94.60
Purchase #7	$85.73	5.682%	$90.6012	$90.60	$90.60	$90.60
7 purchase totals =	$613.23		$647.2357	$647.23	$647.25	$647.30