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	$121.47	12.422%	$136.559	$136.56	$136.55	$136.60
Purchase #2	$245.80	3.116%	$253.4591	$253.46	$253.45	$253.50
Purchase #3	$199.96	12.155%	$224.2651	$224.27	$224.25	$224.30
Purchase #4	$63.47	11.504%	$70.7716	$70.77	$70.75	$70.80
Purchase #5	$125.77	3.434%	$130.0889	$130.09	$130.10	$130.10
Purchase #6	$229.86	11.429%	$256.1307	$256.13	$256.15	$256.10
Purchase #7	$242.49	5.368%	$255.5069	$255.51	$255.50	$255.50
7 purchase totals =	$1,228.82		$1,326.7813	$1,326.79	$1,326.75	$1,326.90