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	$28.75	4.141%	$29.9405	$29.94	$29.95	$29.90
Purchase #2	$123.39	9.418%	$135.0109	$135.01	$135.00	$135.00
Purchase #3	$104.46	4.749%	$109.4208	$109.42	$109.40	$109.40
Purchase #4	$174.58	10.326%	$192.6071	$192.61	$192.60	$192.60
Purchase #5	$85.73	10.147%	$94.429	$94.43	$94.45	$94.40
Purchase #6	$208.39	6.872%	$222.7106	$222.71	$222.70	$222.70
Purchase #7	$234.82	13.538%	$266.6099	$266.61	$266.60	$266.60
7 purchase totals =	$960.12		$1,050.7288	$1,050.73	$1,050.70	$1,050.60