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	$224.30	9.635%	$245.9113	$245.91	$245.90	$245.90
Purchase #2	$159.45	6.808%	$170.3054	$170.31	$170.30	$170.30
Purchase #3	$56.46	13.582%	$64.1284	$64.13	$64.15	$64.10
Purchase #4	$225.66	13.219%	$255.49	$255.49	$255.50	$255.50
Purchase #5	$18.97	13.265%	$21.4864	$21.49	$21.50	$21.50
Purchase #6	$77.53	6.730%	$82.7478	$82.75	$82.75	$82.70
Purchase #7	$225.53	3.622%	$233.6987	$233.70	$233.70	$233.70
7 purchase totals =	$987.90		$1,073.7680	$1,073.78	$1,073.80	$1,073.70