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	$242.91	4.411%	$253.6248	$253.62	$253.60	$253.60
Purchase #2	$123.86	6.821%	$132.3085	$132.31	$132.30	$132.30
Purchase #3	$110.56	7.705%	$119.0786	$119.08	$119.10	$119.10
Purchase #4	$234.66	12.710%	$264.4853	$264.49	$264.50	$264.50
Purchase #5	$227.85	4.701%	$238.5612	$238.56	$238.55	$238.60
Purchase #6	$24.77	12.370%	$27.834	$27.83	$27.85	$27.80
Purchase #7	$97.51	3.508%	$100.9307	$100.93	$100.95	$100.90
7 purchase totals =	$1,062.12		$1,136.8231	$1,136.82	$1,136.85	$1,136.80