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	$118.77	10.485%	$131.223	$131.22	$131.20	$131.20
Purchase #2	$219.82	6.639%	$234.4138	$234.41	$234.40	$234.40
Purchase #3	$58.38	8.386%	$63.2757	$63.28	$63.30	$63.30
Purchase #4	$21.96	12.327%	$24.667	$24.67	$24.65	$24.70
Purchase #5	$109.54	12.333%	$123.0496	$123.05	$123.05	$123.00
Purchase #6	$36.66	10.400%	$40.4726	$40.47	$40.45	$40.50
Purchase #7	$162.25	8.848%	$176.6059	$176.61	$176.60	$176.60
7 purchase totals =	$727.38		$793.7076	$793.71	$793.65	$793.70