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	$199.99	11.223%	$222.4349	$222.43	$222.45	$222.40
Purchase #2	$57.96	10.676%	$64.1478	$64.15	$64.15	$64.10
Purchase #3	$207.53	9.817%	$227.9032	$227.90	$227.90	$227.90
Purchase #4	$96.96	8.678%	$105.3742	$105.37	$105.35	$105.40
Purchase #5	$34.34	12.811%	$38.7393	$38.74	$38.75	$38.70
Purchase #6	$233.68	9.208%	$255.1973	$255.20	$255.20	$255.20
Purchase #7	$82.55	3.493%	$85.4335	$85.43	$85.45	$85.40
7 purchase totals =	$913.01		$999.2302	$999.22	$999.25	$999.10