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	$14.30	9.744%	$15.6934	$15.69	$15.70	$15.70
Purchase #2	$56.55	7.152%	$60.5945	$60.59	$60.60	$60.60
Purchase #3	$237.82	7.596%	$255.8848	$255.88	$255.90	$255.90
Purchase #4	$50.77	11.211%	$56.4618	$56.46	$56.45	$56.50
Purchase #5	$90.40	12.399%	$101.6087	$101.61	$101.60	$101.60
Purchase #6	$55.47	7.322%	$59.5315	$59.53	$59.55	$59.50
Purchase #7	$83.78	10.443%	$92.5291	$92.53	$92.55	$92.50
7 purchase totals =	$589.09		$642.3038	$642.29	$642.35	$642.30