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	$46.78	9.356%	$51.1567	$51.16	$51.15	$51.20
Purchase #2	$145.99	4.721%	$152.8822	$152.88	$152.90	$152.90
Purchase #3	$102.58	5.228%	$107.9429	$107.94	$107.95	$107.90
Purchase #4	$195.35	13.487%	$221.6969	$221.70	$221.70	$221.70
Purchase #5	$73.65	6.626%	$78.53	$78.53	$78.55	$78.50
Purchase #6	$181.61	8.230%	$196.5565	$196.56	$196.55	$196.60
Purchase #7	$134.83	12.871%	$152.184	$152.18	$152.20	$152.20
7 purchase totals =	$880.79		$960.9492	$960.95	$961.00	$961.00