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	$108.37	5.592%	$114.4301	$114.43	$114.45	$114.40
Purchase #2	$149.60	11.333%	$166.5542	$166.55	$166.55	$166.60
Purchase #3	$199.79	10.104%	$219.9768	$219.98	$220.00	$220.00
Purchase #4	$79.67	12.170%	$89.3658	$89.37	$89.35	$89.40
Purchase #5	$57.69	5.751%	$61.0078	$61.01	$61.00	$61.00
Purchase #6	$219.79	11.720%	$245.5494	$245.55	$245.55	$245.50
Purchase #7	$11.94	11.729%	$13.3404	$13.34	$13.35	$13.30
7 purchase totals =	$826.85		$910.2245	$910.23	$910.25	$910.20