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	$110.54	12.620%	$124.4901	$124.49	$124.50	$124.50
Purchase #2	$190.81	12.303%	$214.2854	$214.29	$214.30	$214.30
Purchase #3	$41.89	5.768%	$44.3062	$44.31	$44.30	$44.30
Purchase #4	$85.43	6.111%	$90.6506	$90.65	$90.65	$90.70
Purchase #5	$8.46	12.108%	$9.4843	$9.48	$9.50	$9.50
Purchase #6	$73.56	4.269%	$76.7003	$76.70	$76.70	$76.70
Purchase #7	$95.86	5.123%	$100.7709	$100.77	$100.75	$100.80
7 purchase totals =	$606.55		$660.6878	$660.69	$660.70	$660.80