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	$70.49	5.745%	$74.5397	$74.54	$74.55	$74.50
Purchase #2	$210.39	9.272%	$229.8974	$229.90	$229.90	$229.90
Purchase #3	$53.94	10.459%	$59.5816	$59.58	$59.60	$59.60
Purchase #4	$38.33	3.799%	$39.7862	$39.79	$39.80	$39.80
Purchase #5	$229.40	4.201%	$239.0371	$239.04	$239.05	$239.00
Purchase #6	$126.60	11.635%	$141.3299	$141.33	$141.35	$141.30
Purchase #7	$130.46	8.385%	$141.3991	$141.40	$141.40	$141.40
7 purchase totals =	$859.61		$925.5710	$925.58	$925.65	$925.50