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	$133.58	6.354%	$142.0677	$142.07	$142.05	$142.10
Purchase #2	$121.30	5.488%	$127.9569	$127.96	$127.95	$128.00
Purchase #3	$27.78	6.591%	$29.611	$29.61	$29.60	$29.60
Purchase #4	$167.59	10.151%	$184.6021	$184.60	$184.60	$184.60
Purchase #5	$58.90	9.357%	$64.4113	$64.41	$64.40	$64.40
Purchase #6	$105.61	5.125%	$111.0225	$111.02	$111.00	$111.00
Purchase #7	$13.73	3.333%	$14.1876	$14.19	$14.20	$14.20
7 purchase totals =	$628.49		$673.8591	$673.86	$673.80	$673.90