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	$33.70	10.252%	$37.1549	$37.15	$37.15	$37.20
Purchase #2	$135.67	8.610%	$147.3512	$147.35	$147.35	$147.40
Purchase #3	$146.98	6.721%	$156.8585	$156.86	$156.85	$156.90
Purchase #4	$19.36	5.209%	$20.3685	$20.37	$20.35	$20.40
Purchase #5	$62.79	6.713%	$67.0051	$67.01	$67.00	$67.00
Purchase #6	$12.45	6.560%	$13.2667	$13.27	$13.25	$13.30
Purchase #7	$103.32	10.353%	$114.0167	$114.02	$114.00	$114.00
7 purchase totals =	$514.27		$556.0216	$556.03	$555.95	$556.20