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	$46.89	6.682%	$50.0232	$50.02	$50.00	$50.00
Purchase #2	$109.93	12.698%	$123.8889	$123.89	$123.90	$123.90
Purchase #3	$209.98	13.129%	$237.5483	$237.55	$237.55	$237.50
Purchase #4	$234.28	6.456%	$249.4051	$249.41	$249.40	$249.40
Purchase #5	$80.81	12.498%	$90.9096	$90.91	$90.90	$90.90
Purchase #6	$203.42	12.407%	$228.6583	$228.66	$228.65	$228.70
Purchase #7	$89.83	4.384%	$93.7681	$93.77	$93.75	$93.80
7 purchase totals =	$975.14		$1,074.2015	$1,074.21	$1,074.15	$1,074.20