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	$38.49	10.723%	$42.6173	$42.62	$42.60	$42.60
Purchase #2	$215.48	10.641%	$238.4092	$238.41	$238.40	$238.40
Purchase #3	$91.59	9.303%	$100.1106	$100.11	$100.10	$100.10
Purchase #4	$203.51	7.110%	$217.9796	$217.98	$218.00	$218.00
Purchase #5	$6.90	7.598%	$7.4243	$7.42	$7.40	$7.40
Purchase #6	$150.40	11.231%	$167.2914	$167.29	$167.30	$167.30
Purchase #7	$77.80	12.660%	$87.6495	$87.65	$87.65	$87.60
7 purchase totals =	$784.17		$861.4819	$861.48	$861.45	$861.40