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	$5.88	12.248%	$6.6002	$6.60	$6.60	$6.60
Purchase #2	$70.72	11.585%	$78.9129	$78.91	$78.90	$78.90
Purchase #3	$195.39	11.723%	$218.2956	$218.30	$218.30	$218.30
Purchase #4	$209.72	8.490%	$227.5252	$227.53	$227.55	$227.50
Purchase #5	$53.50	12.785%	$60.34	$60.34	$60.35	$60.30
Purchase #6	$119.40	6.465%	$127.1192	$127.12	$127.10	$127.10
Purchase #7	$145.89	12.265%	$163.7834	$163.78	$163.80	$163.80
7 purchase totals =	$800.50		$882.5765	$882.58	$882.60	$882.50