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	$164.90	12.684%	$185.8159	$185.82	$185.80	$185.80
Purchase #2	$238.99	12.338%	$268.4766	$268.48	$268.50	$268.50
Purchase #3	$187.84	4.586%	$196.4543	$196.45	$196.45	$196.50
Purchase #4	$38.49	3.827%	$39.963	$39.96	$39.95	$40.00
Purchase #5	$87.35	11.124%	$97.0668	$97.07	$97.05	$97.10
Purchase #6	$179.85	13.405%	$203.9589	$203.96	$203.95	$204.00
Purchase #7	$99.74	11.813%	$111.5223	$111.52	$111.50	$111.50
7 purchase totals =	$997.16		$1,103.2578	$1,103.26	$1,103.20	$1,103.40