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	$95.87	4.646%	$100.3241	$100.32	$100.30	$100.30
Purchase #2	$125.44	11.125%	$139.3952	$139.40	$139.40	$139.40
Purchase #3	$167.87	6.189%	$178.2595	$178.26	$178.25	$178.30
Purchase #4	$202.38	10.265%	$223.1543	$223.15	$223.15	$223.20
Purchase #5	$182.48	5.237%	$192.0365	$192.04	$192.05	$192.00
Purchase #6	$51.28	10.867%	$56.8526	$56.85	$56.85	$56.90
Purchase #7	$110.32	11.737%	$123.2683	$123.27	$123.25	$123.30
7 purchase totals =	$935.64		$1,013.2905	$1,013.29	$1,013.25	$1,013.40