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	$109.86	8.786%	$119.5123	$119.51	$119.50	$119.50
Purchase #2	$19.35	10.608%	$21.4026	$21.40	$21.40	$21.40
Purchase #3	$218.88	12.866%	$247.0411	$247.04	$247.05	$247.00
Purchase #4	$37.67	11.132%	$41.8634	$41.86	$41.85	$41.90
Purchase #5	$135.77	12.564%	$152.8281	$152.83	$152.85	$152.80
Purchase #6	$241.68	13.841%	$275.1309	$275.13	$275.15	$275.10
Purchase #7	$56.82	4.783%	$59.5377	$59.54	$59.55	$59.50
7 purchase totals =	$820.03		$917.3161	$917.31	$917.35	$917.20