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	$216.39	9.570%	$237.0985	$237.10	$237.10	$237.10
Purchase #2	$148.77	13.523%	$168.8882	$168.89	$168.90	$168.90
Purchase #3	$127.39	9.468%	$139.4513	$139.45	$139.45	$139.50
Purchase #4	$60.51	7.303%	$64.929	$64.93	$64.95	$64.90
Purchase #5	$131.35	6.374%	$139.7222	$139.72	$139.70	$139.70
Purchase #6	$165.35	11.444%	$184.2727	$184.27	$184.25	$184.30
Purchase #7	$250.82	12.169%	$281.3423	$281.34	$281.35	$281.30
7 purchase totals =	$1,100.58		$1,215.7042	$1,215.70	$1,215.70	$1,215.70