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	$22.69	3.547%	$23.4948	$23.49	$23.50	$23.50
Purchase #2	$68.71	11.281%	$76.4612	$76.46	$76.45	$76.50
Purchase #3	$106.69	12.786%	$120.3314	$120.33	$120.35	$120.30
Purchase #4	$232.56	9.864%	$255.4997	$255.50	$255.50	$255.50
Purchase #5	$54.35	4.757%	$56.9354	$56.94	$56.95	$56.90
Purchase #6	$40.93	12.246%	$45.9423	$45.94	$45.95	$45.90
Purchase #7	$147.42	11.464%	$164.3202	$164.32	$164.30	$164.30
7 purchase totals =	$673.35		$742.9850	$742.98	$743.00	$742.90