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	$86.47	13.232%	$97.9117	$97.91	$97.90	$97.90
Purchase #2	$157.64	3.551%	$163.2378	$163.24	$163.25	$163.20
Purchase #3	$55.38	10.680%	$61.2946	$61.29	$61.30	$61.30
Purchase #4	$37.48	12.340%	$42.105	$42.11	$42.10	$42.10
Purchase #5	$81.85	9.132%	$89.3245	$89.32	$89.30	$89.30
Purchase #6	$100.59	7.586%	$108.2208	$108.22	$108.20	$108.20
Purchase #7	$65.25	8.377%	$70.716	$70.72	$70.70	$70.70
7 purchase totals =	$584.66		$632.8104	$632.81	$632.75	$632.70