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	$51.25	12.580%	$57.6973	$57.70	$57.70	$57.70
Purchase #2	$96.47	9.265%	$105.4079	$105.41	$105.40	$105.40
Purchase #3	$101.60	3.658%	$105.3165	$105.32	$105.30	$105.30
Purchase #4	$200.97	10.659%	$222.3914	$222.39	$222.40	$222.40
Purchase #5	$118.43	10.343%	$130.6792	$130.68	$130.70	$130.70
Purchase #6	$84.39	4.846%	$88.4795	$88.48	$88.50	$88.50
Purchase #7	$7.45	12.479%	$8.3797	$8.38	$8.40	$8.40
7 purchase totals =	$660.56		$718.3515	$718.36	$718.40	$718.40