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	$139.89	8.594%	$151.9121	$151.91	$151.90	$151.90
Purchase #2	$58.57	11.670%	$65.4051	$65.41	$65.40	$65.40
Purchase #3	$97.37	11.801%	$108.8606	$108.86	$108.85	$108.90
Purchase #4	$207.82	6.836%	$222.0266	$222.03	$222.05	$222.00
Purchase #5	$126.82	11.665%	$141.6136	$141.61	$141.60	$141.60
Purchase #6	$38.61	10.265%	$42.5733	$42.57	$42.55	$42.60
Purchase #7	$82.98	11.184%	$92.2605	$92.26	$92.25	$92.30
7 purchase totals =	$752.06		$824.6518	$824.65	$824.60	$824.70