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	$59.44	11.469%	$66.2572	$66.26	$66.25	$66.30
Purchase #2	$78.74	13.657%	$89.4935	$89.49	$89.50	$89.50
Purchase #3	$84.94	9.787%	$93.2531	$93.25	$93.25	$93.30
Purchase #4	$71.96	9.321%	$78.6674	$78.67	$78.65	$78.70
Purchase #5	$9.58	9.736%	$10.5127	$10.51	$10.50	$10.50
Purchase #6	$65.67	7.267%	$70.4422	$70.44	$70.45	$70.40
Purchase #7	$134.30	13.752%	$152.7689	$152.77	$152.75	$152.80
7 purchase totals =	$504.63		$561.3950	$561.39	$561.35	$561.50