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	$39.40	8.594%	$42.786	$42.79	$42.80	$42.80
Purchase #2	$213.30	10.464%	$235.6197	$235.62	$235.60	$235.60
Purchase #3	$140.42	8.769%	$152.7334	$152.73	$152.75	$152.70
Purchase #4	$74.37	5.730%	$78.6314	$78.63	$78.65	$78.60
Purchase #5	$136.81	10.572%	$151.2736	$151.27	$151.25	$151.30
Purchase #6	$188.64	7.798%	$203.3501	$203.35	$203.35	$203.40
Purchase #7	$189.59	5.603%	$200.2127	$200.21	$200.20	$200.20
7 purchase totals =	$982.53		$1,064.6069	$1,064.60	$1,064.60	$1,064.60