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	$173.89	8.119%	$188.0081	$188.01	$188.00	$188.00
Purchase #2	$223.41	5.800%	$236.3678	$236.37	$236.35	$236.40
Purchase #3	$109.38	7.200%	$117.2554	$117.26	$117.25	$117.30
Purchase #4	$28.58	10.824%	$31.6735	$31.67	$31.65	$31.70
Purchase #5	$182.55	7.793%	$196.7761	$196.78	$196.80	$196.80
Purchase #6	$160.97	5.526%	$169.8652	$169.87	$169.85	$169.90
Purchase #7	$137.40	3.240%	$141.8518	$141.85	$141.85	$141.90
7 purchase totals =	$1,016.18		$1,081.7979	$1,081.81	$1,081.75	$1,082.00