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	$7.85	7.817%	$8.4636	$8.46	$8.45	$8.50
Purchase #2	$108.63	7.161%	$116.409	$116.41	$116.40	$116.40
Purchase #3	$87.87	13.676%	$99.8871	$99.89	$99.90	$99.90
Purchase #4	$52.39	3.423%	$54.1833	$54.18	$54.20	$54.20
Purchase #5	$18.68	10.290%	$20.6022	$20.60	$20.60	$20.60
Purchase #6	$28.77	3.691%	$29.8319	$29.83	$29.85	$29.80
Purchase #7	$209.37	9.603%	$229.4758	$229.48	$229.50	$229.50
7 purchase totals =	$513.56		$558.8529	$558.85	$558.90	$558.90