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	$174.31	5.293%	$183.5362	$183.54	$183.55	$183.50
Purchase #2	$57.29	9.858%	$62.9376	$62.94	$62.95	$62.90
Purchase #3	$48.56	13.564%	$55.1467	$55.15	$55.15	$55.10
Purchase #4	$33.34	11.442%	$37.1548	$37.15	$37.15	$37.20
Purchase #5	$53.74	8.386%	$58.2466	$58.25	$58.25	$58.20
Purchase #6	$152.50	4.149%	$158.8272	$158.83	$158.85	$158.80
Purchase #7	$35.50	9.852%	$38.9975	$39.00	$39.00	$39.00
7 purchase totals =	$555.24		$594.8466	$594.86	$594.90	$594.70