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	$102.48	8.666%	$111.3609	$111.36	$111.35	$111.40
Purchase #2	$249.50	10.628%	$276.0169	$276.02	$276.00	$276.00
Purchase #3	$91.29	13.247%	$103.3832	$103.38	$103.40	$103.40
Purchase #4	$84.65	6.191%	$89.8907	$89.89	$89.90	$89.90
Purchase #5	$184.75	7.485%	$198.5785	$198.58	$198.60	$198.60
Purchase #6	$21.26	3.736%	$22.0543	$22.05	$22.05	$22.10
Purchase #7	$64.87	10.709%	$71.8169	$71.82	$71.80	$71.80
7 purchase totals =	$798.80		$873.1014	$873.10	$873.10	$873.20