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	$85.90	3.835%	$89.1943	$89.19	$89.20	$89.20
Purchase #2	$248.25	9.323%	$271.3943	$271.39	$271.40	$271.40
Purchase #3	$226.84	5.434%	$239.1665	$239.17	$239.15	$239.20
Purchase #4	$231.60	13.680%	$263.2829	$263.28	$263.30	$263.30
Purchase #5	$47.36	7.504%	$50.9139	$50.91	$50.90	$50.90
Purchase #6	$160.82	3.352%	$166.2107	$166.21	$166.20	$166.20
Purchase #7	$85.69	4.195%	$89.2847	$89.28	$89.30	$89.30
7 purchase totals =	$1,086.46		$1,169.4473	$1,169.43	$1,169.45	$1,169.50