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	$38.73	4.497%	$40.4717	$40.47	$40.45	$40.50
Purchase #2	$59.69	4.180%	$62.185	$62.19	$62.20	$62.20
Purchase #3	$44.26	13.158%	$50.0837	$50.08	$50.10	$50.10
Purchase #4	$198.78	9.291%	$217.2486	$217.25	$217.25	$217.20
Purchase #5	$8.45	12.663%	$9.52	$9.52	$9.50	$9.50
Purchase #6	$77.35	7.221%	$82.9354	$82.94	$82.95	$82.90
Purchase #7	$165.53	12.158%	$185.6551	$185.66	$185.65	$185.70
7 purchase totals =	$592.79		$648.0995	$648.11	$648.10	$648.10