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	$85.55	5.581%	$90.3245	$90.32	$90.30	$90.30
Purchase #2	$11.38	8.372%	$12.3327	$12.33	$12.35	$12.30
Purchase #3	$162.54	11.409%	$181.0842	$181.08	$181.10	$181.10
Purchase #4	$105.59	5.273%	$111.1578	$111.16	$111.15	$111.20
Purchase #5	$101.32	9.646%	$111.0933	$111.09	$111.10	$111.10
Purchase #6	$102.67	5.542%	$108.36	$108.36	$108.35	$108.40
Purchase #7	$43.73	9.213%	$47.7588	$47.76	$47.75	$47.80
7 purchase totals =	$612.78		$662.1113	$662.10	$662.10	$662.20