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	$82.40	10.283%	$90.8732	$90.87	$90.85	$90.90
Purchase #2	$140.50	3.544%	$145.4793	$145.48	$145.50	$145.50
Purchase #3	$24.56	4.206%	$25.593	$25.59	$25.60	$25.60
Purchase #4	$18.36	3.397%	$18.9837	$18.98	$19.00	$19.00
Purchase #5	$244.59	5.469%	$257.9666	$257.97	$257.95	$258.00
Purchase #6	$27.33	4.482%	$28.5549	$28.55	$28.55	$28.60
Purchase #7	$86.95	13.606%	$98.7804	$98.78	$98.80	$98.80
7 purchase totals =	$624.69		$666.2311	$666.22	$666.25	$666.40