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	$99.78	13.869%	$113.6185	$113.62	$113.60	$113.60
Purchase #2	$108.57	7.711%	$116.9418	$116.94	$116.95	$116.90
Purchase #3	$77.86	7.260%	$83.5126	$83.51	$83.50	$83.50
Purchase #4	$24.95	10.666%	$27.6112	$27.61	$27.60	$27.60
Purchase #5	$6.90	5.840%	$7.303	$7.30	$7.30	$7.30
Purchase #6	$113.66	11.792%	$127.0628	$127.06	$127.05	$127.10
Purchase #7	$183.65	3.437%	$189.9621	$189.96	$189.95	$190.00
7 purchase totals =	$615.37		$666.0120	$666.00	$665.95	$666.00