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	$36.88	8.545%	$40.0314	$40.03	$40.05	$40.00
Purchase #2	$247.88	10.591%	$274.133	$274.13	$274.15	$274.10
Purchase #3	$100.45	8.803%	$109.2926	$109.29	$109.30	$109.30
Purchase #4	$67.83	5.348%	$71.4575	$71.46	$71.45	$71.50
Purchase #5	$224.77	9.198%	$245.4443	$245.44	$245.45	$245.40
Purchase #6	$150.42	5.872%	$159.2527	$159.25	$159.25	$159.30
Purchase #7	$101.53	5.245%	$106.8552	$106.86	$106.85	$106.90
7 purchase totals =	$929.76		$1,006.4667	$1,006.46	$1,006.50	$1,006.50