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	$243.96	10.783%	$270.2662	$270.27	$270.25	$270.30
Purchase #2	$74.75	9.563%	$81.8983	$81.90	$81.90	$81.90
Purchase #3	$118.92	10.534%	$131.447	$131.45	$131.45	$131.40
Purchase #4	$38.36	6.625%	$40.9014	$40.90	$40.90	$40.90
Purchase #5	$28.70	8.284%	$31.0775	$31.08	$31.10	$31.10
Purchase #6	$181.67	5.195%	$191.1078	$191.11	$191.10	$191.10
Purchase #7	$61.77	6.300%	$65.6615	$65.66	$65.65	$65.70
7 purchase totals =	$748.13		$812.3597	$812.37	$812.35	$812.40