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	$135.90	11.102%	$150.9876	$150.99	$151.00	$151.00
Purchase #2	$111.97	6.610%	$119.3712	$119.37	$119.35	$119.40
Purchase #3	$80.54	13.490%	$91.4048	$91.40	$91.40	$91.40
Purchase #4	$217.52	5.713%	$229.9469	$229.95	$229.95	$229.90
Purchase #5	$241.32	8.355%	$261.4823	$261.48	$261.50	$261.50
Purchase #6	$79.74	12.198%	$89.4667	$89.47	$89.45	$89.50
Purchase #7	$19.40	11.307%	$21.5936	$21.59	$21.60	$21.60
7 purchase totals =	$886.39		$964.2531	$964.25	$964.25	$964.30