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	$89.58	6.591%	$95.4842	$95.48	$95.50	$95.50
Purchase #2	$36.47	3.770%	$37.8449	$37.84	$37.85	$37.80
Purchase #3	$147.59	12.613%	$166.2055	$166.21	$166.20	$166.20
Purchase #4	$164.60	9.573%	$180.3572	$180.36	$180.35	$180.40
Purchase #5	$103.83	12.591%	$116.9032	$116.90	$116.90	$116.90
Purchase #6	$233.73	3.687%	$242.3476	$242.35	$242.35	$242.30
Purchase #7	$77.37	4.128%	$80.5638	$80.56	$80.55	$80.60
7 purchase totals =	$853.17		$919.7064	$919.70	$919.70	$919.70