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	$37.98	11.835%	$42.4749	$42.47	$42.45	$42.50
Purchase #2	$211.91	9.604%	$232.2618	$232.26	$232.25	$232.30
Purchase #3	$210.30	3.623%	$217.9192	$217.92	$217.90	$217.90
Purchase #4	$35.29	10.112%	$38.8585	$38.86	$38.85	$38.90
Purchase #5	$181.86	10.300%	$200.5916	$200.59	$200.60	$200.60
Purchase #6	$63.96	4.638%	$66.9265	$66.93	$66.95	$66.90
Purchase #7	$54.57	5.592%	$57.6216	$57.62	$57.60	$57.60
7 purchase totals =	$795.87		$856.6541	$856.65	$856.60	$856.70