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	$241.35	5.844%	$255.4545	$255.45	$255.45	$255.50
Purchase #2	$104.35	4.675%	$109.2284	$109.23	$109.25	$109.20
Purchase #3	$149.94	7.671%	$161.4419	$161.44	$161.45	$161.40
Purchase #4	$90.72	5.275%	$95.5055	$95.51	$95.50	$95.50
Purchase #5	$78.54	3.830%	$81.5481	$81.55	$81.55	$81.50
Purchase #6	$108.38	6.338%	$115.2491	$115.25	$115.25	$115.20
Purchase #7	$94.70	8.694%	$102.9332	$102.93	$102.95	$102.90
7 purchase totals =	$867.98		$921.3607	$921.36	$921.40	$921.20