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	$78.36	6.300%	$83.2967	$83.30	$83.30	$83.30
Purchase #2	$10.63	11.237%	$11.8245	$11.82	$11.80	$11.80
Purchase #3	$82.55	4.678%	$86.4117	$86.41	$86.40	$86.40
Purchase #4	$169.59	9.605%	$185.8791	$185.88	$185.90	$185.90
Purchase #5	$57.82	10.247%	$63.7448	$63.74	$63.75	$63.70
Purchase #6	$76.51	12.422%	$86.0141	$86.01	$86.00	$86.00
Purchase #7	$42.39	4.506%	$44.3001	$44.30	$44.30	$44.30
7 purchase totals =	$517.85		$561.4710	$561.46	$561.45	$561.40