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	$78.49	6.584%	$83.6578	$83.66	$83.65	$83.70
Purchase #2	$231.48	5.816%	$244.9429	$244.94	$244.95	$244.90
Purchase #3	$208.28	12.110%	$233.5027	$233.50	$233.50	$233.50
Purchase #4	$96.49	13.115%	$109.1447	$109.14	$109.15	$109.10
Purchase #5	$127.43	12.188%	$142.9612	$142.96	$142.95	$143.00
Purchase #6	$225.65	9.783%	$247.7253	$247.73	$247.75	$247.70
Purchase #7	$150.83	3.357%	$155.8934	$155.89	$155.90	$155.90
7 purchase totals =	$1,118.65		$1,217.8280	$1,217.82	$1,217.85	$1,217.80