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	$38.46	3.723%	$39.8919	$39.89	$39.90	$39.90
Purchase #2	$239.25	10.485%	$264.3354	$264.34	$264.35	$264.30
Purchase #3	$112.43	12.849%	$126.8761	$126.88	$126.90	$126.90
Purchase #4	$92.38	8.538%	$100.2674	$100.27	$100.25	$100.30
Purchase #5	$200.44	12.151%	$224.7955	$224.80	$224.80	$224.80
Purchase #6	$14.61	12.550%	$16.4436	$16.44	$16.45	$16.40
Purchase #7	$196.48	13.198%	$222.4114	$222.41	$222.40	$222.40
7 purchase totals =	$894.05		$995.0213	$995.03	$995.05	$995.00