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	$239.64	12.646%	$269.9449	$269.94	$269.95	$269.90
Purchase #2	$126.61	7.698%	$136.3564	$136.36	$136.35	$136.40
Purchase #3	$247.75	13.623%	$281.501	$281.50	$281.50	$281.50
Purchase #4	$53.39	11.149%	$59.3425	$59.34	$59.35	$59.30
Purchase #5	$221.27	5.666%	$233.8072	$233.81	$233.80	$233.80
Purchase #6	$227.50	4.471%	$237.6715	$237.67	$237.65	$237.70
Purchase #7	$111.73	5.843%	$118.2584	$118.26	$118.25	$118.30
7 purchase totals =	$1,227.89		$1,336.8819	$1,336.88	$1,336.85	$1,336.90