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	$183.30	12.275%	$205.8001	$205.80	$205.80	$205.80
Purchase #2	$71.62	12.385%	$80.4901	$80.49	$80.50	$80.50
Purchase #3	$114.94	10.295%	$126.7731	$126.77	$126.75	$126.80
Purchase #4	$128.37	10.690%	$142.0928	$142.09	$142.10	$142.10
Purchase #5	$30.47	8.138%	$32.9496	$32.95	$32.95	$32.90
Purchase #6	$18.90	13.375%	$21.4279	$21.43	$21.45	$21.40
Purchase #7	$205.31	8.570%	$222.9051	$222.91	$222.90	$222.90
7 purchase totals =	$752.91		$832.4387	$832.44	$832.45	$832.40