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	$126.58	12.534%	$142.4455	$142.45	$142.45	$142.40
Purchase #2	$193.77	9.720%	$212.6044	$212.60	$212.60	$212.60
Purchase #3	$100.43	10.116%	$110.5895	$110.59	$110.60	$110.60
Purchase #4	$223.86	9.800%	$245.7983	$245.80	$245.80	$245.80
Purchase #5	$155.78	7.834%	$167.9838	$167.98	$168.00	$168.00
Purchase #6	$203.32	10.173%	$224.0037	$224.00	$224.00	$224.00
Purchase #7	$196.44	11.242%	$218.5238	$218.52	$218.50	$218.50
7 purchase totals =	$1,200.18		$1,321.9490	$1,321.94	$1,321.95	$1,321.90