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	$154.51	6.305%	$164.2519	$164.25	$164.25	$164.30
Purchase #2	$221.45	3.221%	$228.5829	$228.58	$228.60	$228.60
Purchase #3	$224.35	9.190%	$244.9678	$244.97	$244.95	$245.00
Purchase #4	$55.45	8.235%	$60.0163	$60.02	$60.00	$60.00
Purchase #5	$82.38	3.799%	$85.5096	$85.51	$85.50	$85.50
Purchase #6	$209.39	8.660%	$227.5232	$227.52	$227.50	$227.50
Purchase #7	$52.79	4.346%	$55.0843	$55.08	$55.10	$55.10
7 purchase totals =	$1,000.32		$1,065.9360	$1,065.93	$1,065.90	$1,066.00