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	$96.32	13.758%	$109.5717	$109.57	$109.55	$109.60
Purchase #2	$127.51	8.290%	$138.0806	$138.08	$138.10	$138.10
Purchase #3	$149.94	4.532%	$156.7353	$156.74	$156.75	$156.70
Purchase #4	$94.36	9.274%	$103.1109	$103.11	$103.10	$103.10
Purchase #5	$145.84	13.102%	$164.948	$164.95	$164.95	$164.90
Purchase #6	$202.48	12.600%	$227.9925	$227.99	$228.00	$228.00
Purchase #7	$92.91	8.135%	$100.4682	$100.47	$100.45	$100.50
7 purchase totals =	$909.36		$1,000.9072	$1,000.91	$1,000.90	$1,000.90