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	$61.30	8.438%	$66.4725	$66.47	$66.45	$66.50
Purchase #2	$169.33	9.154%	$184.8305	$184.83	$184.85	$184.80
Purchase #3	$48.79	11.638%	$54.4682	$54.47	$54.45	$54.50
Purchase #4	$64.90	12.263%	$72.8587	$72.86	$72.85	$72.90
Purchase #5	$66.88	4.262%	$69.7304	$69.73	$69.75	$69.70
Purchase #6	$5.47	3.463%	$5.6594	$5.66	$5.65	$5.70
Purchase #7	$109.84	13.254%	$124.3982	$124.40	$124.40	$124.40
7 purchase totals =	$526.51		$578.4179	$578.42	$578.40	$578.50