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	$32.93	12.802%	$37.1457	$37.15	$37.15	$37.10
Purchase #2	$229.68	10.280%	$253.2911	$253.29	$253.30	$253.30
Purchase #3	$135.54	4.369%	$141.4617	$141.46	$141.45	$141.50
Purchase #4	$150.74	5.174%	$158.5393	$158.54	$158.55	$158.50
Purchase #5	$44.40	9.381%	$48.5652	$48.57	$48.55	$48.60
Purchase #6	$196.32	11.744%	$219.3758	$219.38	$219.40	$219.40
Purchase #7	$111.98	8.495%	$121.4927	$121.49	$121.50	$121.50
7 purchase totals =	$901.59		$979.8715	$979.88	$979.90	$979.90