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	$98.77	13.472%	$112.0763	$112.08	$112.10	$112.10
Purchase #2	$11.43	8.788%	$12.4345	$12.43	$12.45	$12.40
Purchase #3	$25.26	13.301%	$28.6198	$28.62	$28.60	$28.60
Purchase #4	$135.62	6.339%	$144.217	$144.22	$144.20	$144.20
Purchase #5	$80.76	10.546%	$89.2769	$89.28	$89.30	$89.30
Purchase #6	$63.55	7.542%	$68.3429	$68.34	$68.35	$68.30
Purchase #7	$245.46	4.643%	$256.8567	$256.86	$256.85	$256.90
7 purchase totals =	$660.85		$711.8241	$711.83	$711.85	$711.80