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	$16.78	9.546%	$18.3818	$18.38	$18.40	$18.40
Purchase #2	$248.85	13.142%	$281.5539	$281.55	$281.55	$281.60
Purchase #3	$215.44	6.340%	$229.0989	$229.10	$229.10	$229.10
Purchase #4	$11.91	11.709%	$13.3045	$13.30	$13.30	$13.30
Purchase #5	$83.29	7.461%	$89.5043	$89.50	$89.50	$89.50
Purchase #6	$213.36	13.213%	$241.5513	$241.55	$241.55	$241.60
Purchase #7	$6.82	13.839%	$7.7638	$7.76	$7.75	$7.80
7 purchase totals =	$796.45		$881.1585	$881.14	$881.15	$881.30