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	$51.58	4.728%	$54.0187	$54.02	$54.00	$54.00
Purchase #2	$72.40	5.481%	$76.3682	$76.37	$76.35	$76.40
Purchase #3	$99.65	13.374%	$112.9772	$112.98	$113.00	$113.00
Purchase #4	$80.82	3.782%	$83.8766	$83.88	$83.90	$83.90
Purchase #5	$84.32	4.339%	$87.9786	$87.98	$88.00	$88.00
Purchase #6	$67.47	13.439%	$76.5373	$76.54	$76.55	$76.50
Purchase #7	$145.73	12.622%	$164.124	$164.12	$164.10	$164.10
7 purchase totals =	$601.97		$655.8806	$655.89	$655.90	$655.90