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	$28.49	5.618%	$30.0906	$30.09	$30.10	$30.10
Purchase #2	$111.93	10.436%	$123.611	$123.61	$123.60	$123.60
Purchase #3	$33.35	12.567%	$37.5411	$37.54	$37.55	$37.50
Purchase #4	$197.80	4.865%	$207.423	$207.42	$207.40	$207.40
Purchase #5	$59.94	8.783%	$65.2045	$65.20	$65.20	$65.20
Purchase #6	$153.80	5.521%	$162.2913	$162.29	$162.30	$162.30
Purchase #7	$153.79	13.442%	$174.4625	$174.46	$174.45	$174.50
7 purchase totals =	$739.10		$800.6240	$800.61	$800.60	$800.60