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	$75.74	12.676%	$85.3408	$85.34	$85.35	$85.30
Purchase #2	$85.28	6.329%	$90.6774	$90.68	$90.70	$90.70
Purchase #3	$98.89	5.569%	$104.3972	$104.40	$104.40	$104.40
Purchase #4	$72.63	10.327%	$80.1305	$80.13	$80.15	$80.10
Purchase #5	$21.95	12.454%	$24.6837	$24.68	$24.70	$24.70
Purchase #6	$231.35	10.357%	$255.3109	$255.31	$255.30	$255.30
Purchase #7	$176.75	5.179%	$185.9039	$185.90	$185.90	$185.90
7 purchase totals =	$762.59		$826.4444	$826.44	$826.50	$826.40