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	$136.72	3.346%	$141.2947	$141.29	$141.30	$141.30
Purchase #2	$59.60	5.426%	$62.8339	$62.83	$62.85	$62.80
Purchase #3	$82.44	4.431%	$86.0929	$86.09	$86.10	$86.10
Purchase #4	$219.95	6.157%	$233.4923	$233.49	$233.50	$233.50
Purchase #5	$240.97	8.758%	$262.0742	$262.07	$262.05	$262.10
Purchase #6	$184.77	13.555%	$209.8156	$209.82	$209.80	$209.80
Purchase #7	$156.35	4.189%	$162.8995	$162.90	$162.90	$162.90
7 purchase totals =	$1,080.80		$1,158.5031	$1,158.49	$1,158.50	$1,158.50