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	$74.33	4.828%	$77.9187	$77.92	$77.90	$77.90
Purchase #2	$121.82	8.255%	$131.8762	$131.88	$131.90	$131.90
Purchase #3	$231.61	6.591%	$246.8754	$246.88	$246.90	$246.90
Purchase #4	$69.36	6.835%	$74.1008	$74.10	$74.10	$74.10
Purchase #5	$18.54	13.627%	$21.0664	$21.07	$21.05	$21.10
Purchase #6	$59.45	4.635%	$62.2055	$62.21	$62.20	$62.20
Purchase #7	$97.32	11.443%	$108.4563	$108.46	$108.45	$108.50
7 purchase totals =	$672.43		$722.4993	$722.52	$722.50	$722.60