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	$99.26	4.116%	$103.3455	$103.35	$103.35	$103.30
Purchase #2	$39.56	10.874%	$43.8618	$43.86	$43.85	$43.90
Purchase #3	$51.47	13.767%	$58.5559	$58.56	$58.55	$58.60
Purchase #4	$81.34	9.836%	$89.3406	$89.34	$89.35	$89.30
Purchase #5	$58.87	7.213%	$63.1163	$63.12	$63.10	$63.10
Purchase #6	$243.85	5.599%	$257.5032	$257.50	$257.50	$257.50
Purchase #7	$205.58	12.460%	$231.1953	$231.20	$231.20	$231.20
7 purchase totals =	$779.93		$846.9186	$846.93	$846.90	$846.90