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	$45.71	11.466%	$50.9511	$50.95	$50.95	$51.00
Purchase #2	$83.56	13.827%	$95.1138	$95.11	$95.10	$95.10
Purchase #3	$100.39	4.530%	$104.9377	$104.94	$104.95	$104.90
Purchase #4	$43.56	9.528%	$47.7104	$47.71	$47.70	$47.70
Purchase #5	$63.60	12.481%	$71.5379	$71.54	$71.55	$71.50
Purchase #6	$131.44	12.716%	$148.1539	$148.15	$148.15	$148.20
Purchase #7	$64.46	5.431%	$67.9608	$67.96	$67.95	$68.00
7 purchase totals =	$532.72		$586.3656	$586.36	$586.35	$586.40