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	$146.85	12.737%	$165.5543	$165.55	$165.55	$165.60
Purchase #2	$158.39	6.368%	$168.4763	$168.48	$168.50	$168.50
Purchase #3	$179.34	4.276%	$187.0086	$187.01	$187.00	$187.00
Purchase #4	$169.52	9.537%	$185.6871	$185.69	$185.70	$185.70
Purchase #5	$32.99	3.276%	$34.0708	$34.07	$34.05	$34.10
Purchase #6	$234.75	10.693%	$259.8518	$259.85	$259.85	$259.90
Purchase #7	$85.74	12.292%	$96.2792	$96.28	$96.30	$96.30
7 purchase totals =	$1,007.58		$1,096.9281	$1,096.93	$1,096.95	$1,097.10