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	$139.57	12.317%	$156.7608	$156.76	$156.75	$156.80
Purchase #2	$40.88	12.198%	$45.8665	$45.87	$45.85	$45.90
Purchase #3	$141.25	5.250%	$148.6656	$148.67	$148.65	$148.70
Purchase #4	$38.88	13.723%	$44.2155	$44.22	$44.20	$44.20
Purchase #5	$148.27	4.654%	$155.1705	$155.17	$155.15	$155.20
Purchase #6	$145.48	9.357%	$159.0926	$159.09	$159.10	$159.10
Purchase #7	$202.58	10.216%	$223.2756	$223.28	$223.30	$223.30
7 purchase totals =	$856.91		$933.0471	$933.06	$933.00	$933.20