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	$75.73	6.393%	$80.5714	$80.57	$80.55	$80.60
Purchase #2	$198.47	11.315%	$220.9269	$220.93	$220.95	$220.90
Purchase #3	$19.30	13.853%	$21.9736	$21.97	$21.95	$22.00
Purchase #4	$34.59	9.192%	$37.7695	$37.77	$37.75	$37.80
Purchase #5	$54.90	8.283%	$59.4474	$59.45	$59.45	$59.40
Purchase #6	$117.88	11.761%	$131.7439	$131.74	$131.75	$131.70
Purchase #7	$16.82	11.282%	$18.7176	$18.72	$18.70	$18.70
7 purchase totals =	$517.69		$571.1503	$571.15	$571.10	$571.10