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	$46.34	9.285%	$50.6427	$50.64	$50.65	$50.60
Purchase #2	$149.55	10.183%	$164.7787	$164.78	$164.80	$164.80
Purchase #3	$74.33	8.220%	$80.4399	$80.44	$80.45	$80.40
Purchase #4	$34.83	4.210%	$36.2963	$36.30	$36.30	$36.30
Purchase #5	$113.98	11.323%	$126.886	$126.89	$126.90	$126.90
Purchase #6	$43.42	3.536%	$44.9553	$44.96	$44.95	$45.00
Purchase #7	$142.61	13.706%	$162.1561	$162.16	$162.15	$162.20
7 purchase totals =	$605.06		$666.1550	$666.17	$666.20	$666.20