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	$6.55	13.270%	$7.4192	$7.42	$7.40	$7.40
Purchase #2	$111.46	3.632%	$115.5082	$115.51	$115.50	$115.50
Purchase #3	$83.78	6.273%	$89.0355	$89.04	$89.05	$89.00
Purchase #4	$153.37	12.797%	$172.9968	$173.00	$173.00	$173.00
Purchase #5	$136.51	4.199%	$142.2421	$142.24	$142.25	$142.20
Purchase #6	$229.32	10.148%	$252.5914	$252.59	$252.60	$252.60
Purchase #7	$162.89	6.651%	$173.7238	$173.72	$173.70	$173.70
7 purchase totals =	$883.88		$953.5170	$953.52	$953.50	$953.40