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	$86.52	3.815%	$89.8207	$89.82	$89.80	$89.80
Purchase #2	$81.98	6.568%	$87.3644	$87.36	$87.35	$87.40
Purchase #3	$12.57	7.746%	$13.5437	$13.54	$13.55	$13.50
Purchase #4	$40.28	5.247%	$42.3935	$42.39	$42.40	$42.40
Purchase #5	$69.73	4.333%	$72.7514	$72.75	$72.75	$72.80
Purchase #6	$21.97	7.411%	$23.5982	$23.60	$23.60	$23.60
Purchase #7	$92.79	3.516%	$96.0525	$96.05	$96.05	$96.10
7 purchase totals =	$405.84		$425.5244	$425.51	$425.50	$425.60