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	$66.56	8.652%	$72.3188	$72.32	$72.30	$72.30
Purchase #2	$147.84	6.709%	$157.7586	$157.76	$157.75	$157.80
Purchase #3	$48.81	10.410%	$53.8911	$53.89	$53.90	$53.90
Purchase #4	$40.66	13.455%	$46.1308	$46.13	$46.15	$46.10
Purchase #5	$246.89	12.561%	$277.9019	$277.90	$277.90	$277.90
Purchase #6	$89.38	9.860%	$98.1929	$98.19	$98.20	$98.20
Purchase #7	$204.71	7.235%	$219.5208	$219.52	$219.50	$219.50
7 purchase totals =	$844.85		$925.7149	$925.71	$925.70	$925.70