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	$49.30	12.564%	$55.4941	$55.49	$55.50	$55.50
Purchase #2	$246.30	6.788%	$263.0188	$263.02	$263.00	$263.00
Purchase #3	$92.26	6.850%	$98.5798	$98.58	$98.60	$98.60
Purchase #4	$53.31	7.508%	$57.3125	$57.31	$57.30	$57.30
Purchase #5	$6.57	12.588%	$7.397	$7.40	$7.40	$7.40
Purchase #6	$72.55	13.709%	$82.4959	$82.50	$82.50	$82.50
Purchase #7	$97.62	8.340%	$105.7615	$105.76	$105.75	$105.80
7 purchase totals =	$617.91		$670.0596	$670.06	$670.05	$670.10