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	$37.96	6.785%	$40.5356	$40.54	$40.55	$40.50
Purchase #2	$87.76	11.757%	$98.0779	$98.08	$98.10	$98.10
Purchase #3	$110.33	5.180%	$116.0451	$116.05	$116.05	$116.00
Purchase #4	$9.65	6.466%	$10.274	$10.27	$10.25	$10.30
Purchase #5	$131.70	6.752%	$140.5924	$140.59	$140.60	$140.60
Purchase #6	$19.33	9.609%	$21.1874	$21.19	$21.20	$21.20
Purchase #7	$104.91	4.791%	$109.9362	$109.94	$109.95	$109.90
7 purchase totals =	$501.64		$536.6486	$536.66	$536.70	$536.60