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	$123.35	10.568%	$136.3856	$136.39	$136.40	$136.40
Purchase #2	$154.56	9.223%	$168.8151	$168.82	$168.80	$168.80
Purchase #3	$128.47	11.132%	$142.7713	$142.77	$142.75	$142.80
Purchase #4	$91.93	8.434%	$99.6834	$99.68	$99.70	$99.70
Purchase #5	$36.87	3.373%	$38.1136	$38.11	$38.10	$38.10
Purchase #6	$246.51	4.831%	$258.4189	$258.42	$258.40	$258.40
Purchase #7	$217.63	5.138%	$228.8118	$228.81	$228.80	$228.80
7 purchase totals =	$999.32		$1,072.9997	$1,073.00	$1,072.95	$1,073.00