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	$49.84	6.635%	$53.1469	$53.15	$53.15	$53.10
Purchase #2	$127.32	13.475%	$144.4764	$144.48	$144.50	$144.50
Purchase #3	$125.58	12.508%	$141.2875	$141.29	$141.30	$141.30
Purchase #4	$243.77	5.647%	$257.5357	$257.54	$257.55	$257.50
Purchase #5	$143.26	4.857%	$150.2181	$150.22	$150.20	$150.20
Purchase #6	$121.51	11.770%	$135.8117	$135.81	$135.80	$135.80
Purchase #7	$52.80	12.526%	$59.4137	$59.41	$59.40	$59.40
7 purchase totals =	$864.08		$941.8900	$941.90	$941.90	$941.80