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	$27.71	6.514%	$29.515	$29.52	$29.50	$29.50
Purchase #2	$243.35	6.274%	$258.6178	$258.62	$258.60	$258.60
Purchase #3	$93.27	9.206%	$101.8564	$101.86	$101.85	$101.90
Purchase #4	$191.62	3.235%	$197.8189	$197.82	$197.80	$197.80
Purchase #5	$248.83	9.157%	$271.6154	$271.62	$271.60	$271.60
Purchase #6	$85.61	4.317%	$89.3058	$89.31	$89.30	$89.30
Purchase #7	$83.75	8.391%	$90.7775	$90.78	$90.80	$90.80
7 purchase totals =	$974.14		$1,039.5068	$1,039.53	$1,039.45	$1,039.50