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	$11.73	5.435%	$12.3675	$12.37	$12.35	$12.40
Purchase #2	$224.57	13.579%	$255.0644	$255.06	$255.05	$255.10
Purchase #3	$139.49	10.495%	$154.1295	$154.13	$154.15	$154.10
Purchase #4	$31.94	8.127%	$34.5358	$34.54	$34.55	$34.50
Purchase #5	$162.40	10.786%	$179.9165	$179.92	$179.90	$179.90
Purchase #6	$168.50	8.504%	$182.8292	$182.83	$182.85	$182.80
Purchase #7	$246.92	3.121%	$254.6264	$254.63	$254.65	$254.60
7 purchase totals =	$985.55		$1,073.4693	$1,073.48	$1,073.50	$1,073.40