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	$88.26	13.725%	$100.3737	$100.37	$100.35	$100.40
Purchase #2	$90.60	5.184%	$95.2967	$95.30	$95.30	$95.30
Purchase #3	$82.30	8.351%	$89.1729	$89.17	$89.15	$89.20
Purchase #4	$92.28	8.489%	$100.1136	$100.11	$100.10	$100.10
Purchase #5	$25.94	9.762%	$28.4723	$28.47	$28.45	$28.50
Purchase #6	$239.56	7.238%	$256.8994	$256.90	$256.90	$256.90
Purchase #7	$128.45	10.675%	$142.162	$142.16	$142.15	$142.20
7 purchase totals =	$747.39		$812.4906	$812.48	$812.40	$812.60