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	$40.41	6.772%	$43.1466	$43.15	$43.15	$43.10
Purchase #2	$169.66	7.827%	$182.9393	$182.94	$182.95	$182.90
Purchase #3	$230.80	10.340%	$254.6647	$254.66	$254.65	$254.70
Purchase #4	$58.79	9.209%	$64.204	$64.20	$64.20	$64.20
Purchase #5	$51.54	10.765%	$57.0883	$57.09	$57.10	$57.10
Purchase #6	$101.49	12.269%	$113.9418	$113.94	$113.95	$113.90
Purchase #7	$173.61	13.254%	$196.6203	$196.62	$196.60	$196.60
7 purchase totals =	$826.30		$912.6050	$912.60	$912.60	$912.50