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	$154.92	6.431%	$164.8829	$164.88	$164.90	$164.90
Purchase #2	$104.68	6.401%	$111.3806	$111.38	$111.40	$111.40
Purchase #3	$155.43	9.165%	$169.6752	$169.68	$169.70	$169.70
Purchase #4	$190.71	10.797%	$211.301	$211.30	$211.30	$211.30
Purchase #5	$152.78	9.205%	$166.8434	$166.84	$166.85	$166.80
Purchase #6	$136.51	3.346%	$141.0776	$141.08	$141.10	$141.10
Purchase #7	$203.74	4.675%	$213.2648	$213.26	$213.25	$213.30
7 purchase totals =	$1,098.77		$1,178.4255	$1,178.42	$1,178.50	$1,178.50