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	$45.66	10.727%	$50.5579	$50.56	$50.55	$50.60
Purchase #2	$21.70	7.644%	$23.3587	$23.36	$23.35	$23.40
Purchase #3	$38.52	6.822%	$41.1478	$41.15	$41.15	$41.10
Purchase #4	$74.72	10.702%	$82.7165	$82.72	$82.70	$82.70
Purchase #5	$31.90	12.679%	$35.9446	$35.94	$35.95	$35.90
Purchase #6	$209.81	7.644%	$225.8479	$225.85	$225.85	$225.80
Purchase #7	$234.72	8.832%	$255.4505	$255.45	$255.45	$255.50
7 purchase totals =	$657.03		$715.0239	$715.03	$715.00	$715.00