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	$73.87	12.494%	$83.0993	$83.10	$83.10	$83.10
Purchase #2	$237.42	7.492%	$255.2075	$255.21	$255.20	$255.20
Purchase #3	$16.50	12.202%	$18.5133	$18.51	$18.50	$18.50
Purchase #4	$142.91	4.850%	$149.8411	$149.84	$149.85	$149.80
Purchase #5	$239.82	6.532%	$255.485	$255.49	$255.50	$255.50
Purchase #6	$113.33	5.773%	$119.8725	$119.87	$119.85	$119.90
Purchase #7	$212.88	13.659%	$241.9573	$241.96	$241.95	$242.00
7 purchase totals =	$1,036.73		$1,123.9760	$1,123.98	$1,123.95	$1,124.00