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	$170.45	8.584%	$185.0814	$185.08	$185.10	$185.10
Purchase #2	$112.86	3.714%	$117.0516	$117.05	$117.05	$117.10
Purchase #3	$126.96	10.361%	$140.1143	$140.11	$140.10	$140.10
Purchase #4	$29.83	5.287%	$31.4071	$31.41	$31.40	$31.40
Purchase #5	$89.44	10.547%	$98.8732	$98.87	$98.85	$98.90
Purchase #6	$85.34	5.826%	$90.3119	$90.31	$90.30	$90.30
Purchase #7	$70.74	12.456%	$79.5514	$79.55	$79.55	$79.60
7 purchase totals =	$685.62		$742.3909	$742.38	$742.35	$742.50