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	$167.99	10.423%	$185.4996	$185.50	$185.50	$185.50
Purchase #2	$149.85	13.397%	$169.9254	$169.93	$169.95	$169.90
Purchase #3	$101.33	4.543%	$105.9334	$105.93	$105.95	$105.90
Purchase #4	$67.59	9.127%	$73.7589	$73.76	$73.75	$73.80
Purchase #5	$111.90	4.183%	$116.5808	$116.58	$116.60	$116.60
Purchase #6	$145.60	7.209%	$156.0963	$156.10	$156.10	$156.10
Purchase #7	$173.79	6.372%	$184.8639	$184.86	$184.85	$184.90
7 purchase totals =	$918.05		$992.6583	$992.66	$992.70	$992.70