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	$96.79	3.566%	$100.2415	$100.24	$100.25	$100.20
Purchase #2	$225.34	13.873%	$256.6014	$256.60	$256.60	$256.60
Purchase #3	$113.39	4.372%	$118.3474	$118.35	$118.35	$118.30
Purchase #4	$167.43	12.272%	$187.977	$187.98	$188.00	$188.00
Purchase #5	$229.47	10.546%	$253.6699	$253.67	$253.65	$253.70
Purchase #6	$39.90	10.124%	$43.9395	$43.94	$43.95	$43.90
Purchase #7	$85.92	12.776%	$96.8971	$96.90	$96.90	$96.90
7 purchase totals =	$958.24		$1,057.6738	$1,057.68	$1,057.70	$1,057.60