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	$120.61	3.148%	$124.4068	$124.41	$124.40	$124.40
Purchase #2	$52.95	3.132%	$54.6084	$54.61	$54.60	$54.60
Purchase #3	$169.96	11.222%	$189.0329	$189.03	$189.05	$189.00
Purchase #4	$13.36	4.245%	$13.9271	$13.93	$13.95	$13.90
Purchase #5	$132.36	5.694%	$139.8966	$139.90	$139.90	$139.90
Purchase #6	$57.88	12.750%	$65.2597	$65.26	$65.25	$65.30
Purchase #7	$57.68	3.445%	$59.6671	$59.67	$59.65	$59.70
7 purchase totals =	$604.80		$646.7986	$646.81	$646.80	$646.80