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	$52.48	5.291%	$55.2567	$55.26	$55.25	$55.30
Purchase #2	$137.39	4.351%	$143.3678	$143.37	$143.35	$143.40
Purchase #3	$231.67	8.367%	$251.0538	$251.05	$251.05	$251.10
Purchase #4	$165.33	10.179%	$182.1589	$182.16	$182.15	$182.20
Purchase #5	$233.34	13.470%	$264.7709	$264.77	$264.75	$264.80
Purchase #6	$118.89	3.783%	$123.3876	$123.39	$123.40	$123.40
Purchase #7	$143.81	9.129%	$156.9384	$156.94	$156.95	$156.90
7 purchase totals =	$1,082.91		$1,176.9341	$1,176.94	$1,176.90	$1,177.10