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	$51.63	9.554%	$56.5627	$56.56	$56.55	$56.60
Purchase #2	$116.55	11.156%	$129.5523	$129.55	$129.55	$129.60
Purchase #3	$191.86	12.470%	$215.7849	$215.78	$215.80	$215.80
Purchase #4	$250.74	7.682%	$270.0018	$270.00	$270.00	$270.00
Purchase #5	$11.57	6.646%	$12.3389	$12.34	$12.35	$12.30
Purchase #6	$54.48	12.123%	$61.0846	$61.08	$61.10	$61.10
Purchase #7	$186.63	5.291%	$196.5046	$196.50	$196.50	$196.50
7 purchase totals =	$863.46		$941.8298	$941.81	$941.85	$941.90