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	$229.69	8.186%	$248.4924	$248.49	$248.50	$248.50
Purchase #2	$6.82	11.241%	$7.5866	$7.59	$7.60	$7.60
Purchase #3	$224.89	12.360%	$252.6864	$252.69	$252.70	$252.70
Purchase #4	$46.38	13.234%	$52.5179	$52.52	$52.50	$52.50
Purchase #5	$12.39	4.357%	$12.9298	$12.93	$12.95	$12.90
Purchase #6	$137.50	9.370%	$150.3838	$150.38	$150.40	$150.40
Purchase #7	$72.67	10.392%	$80.2219	$80.22	$80.20	$80.20
7 purchase totals =	$730.34		$804.8188	$804.82	$804.85	$804.80