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	$161.81	5.784%	$171.1691	$171.17	$171.15	$171.20
Purchase #2	$123.25	9.481%	$134.9353	$134.94	$134.95	$134.90
Purchase #3	$105.30	4.352%	$109.8827	$109.88	$109.90	$109.90
Purchase #4	$186.91	12.235%	$209.7784	$209.78	$209.80	$209.80
Purchase #5	$5.35	6.250%	$5.6844	$5.68	$5.70	$5.70
Purchase #6	$209.53	11.665%	$233.9717	$233.97	$233.95	$234.00
Purchase #7	$105.53	5.241%	$111.0608	$111.06	$111.05	$111.10
7 purchase totals =	$897.68		$976.4824	$976.48	$976.50	$976.60