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	$166.46	8.224%	$180.1497	$180.15	$180.15	$180.10
Purchase #2	$181.27	13.125%	$205.0617	$205.06	$205.05	$205.10
Purchase #3	$62.61	6.309%	$66.5601	$66.56	$66.55	$66.60
Purchase #4	$177.96	7.819%	$191.8747	$191.87	$191.85	$191.90
Purchase #5	$55.49	7.308%	$59.5452	$59.55	$59.55	$59.50
Purchase #6	$125.53	8.404%	$136.0795	$136.08	$136.10	$136.10
Purchase #7	$86.56	4.594%	$90.5366	$90.54	$90.55	$90.50
7 purchase totals =	$855.88		$929.8075	$929.81	$929.80	$929.80