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	$72.55	10.785%	$80.3745	$80.37	$80.35	$80.40
Purchase #2	$190.35	13.578%	$216.1957	$216.20	$216.20	$216.20
Purchase #3	$117.71	8.630%	$127.8684	$127.87	$127.85	$127.90
Purchase #4	$58.91	4.253%	$61.4154	$61.42	$61.40	$61.40
Purchase #5	$24.30	12.682%	$27.3817	$27.38	$27.40	$27.40
Purchase #6	$69.55	9.129%	$75.8992	$75.90	$75.90	$75.90
Purchase #7	$61.81	5.438%	$65.1712	$65.17	$65.15	$65.20
7 purchase totals =	$595.18		$654.3061	$654.31	$654.25	$654.40