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	$89.55	10.317%	$98.7889	$98.79	$98.80	$98.80
Purchase #2	$33.83	10.267%	$37.3033	$37.30	$37.30	$37.30
Purchase #3	$38.30	6.724%	$40.8753	$40.88	$40.90	$40.90
Purchase #4	$68.64	12.558%	$77.2598	$77.26	$77.25	$77.30
Purchase #5	$155.55	11.240%	$173.0338	$173.03	$173.05	$173.00
Purchase #6	$55.83	3.714%	$57.9035	$57.90	$57.90	$57.90
Purchase #7	$208.80	6.796%	$222.99	$222.99	$223.00	$223.00
7 purchase totals =	$650.50		$708.1546	$708.15	$708.20	$708.20