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	$65.39	3.862%	$67.9154	$67.92	$67.90	$67.90
Purchase #2	$112.83	9.639%	$123.7057	$123.71	$123.70	$123.70
Purchase #3	$80.98	5.365%	$85.3246	$85.32	$85.30	$85.30
Purchase #4	$166.98	13.104%	$188.8611	$188.86	$188.85	$188.90
Purchase #5	$92.42	12.631%	$104.0936	$104.09	$104.10	$104.10
Purchase #6	$201.78	8.869%	$219.6759	$219.68	$219.70	$219.70
Purchase #7	$160.43	13.190%	$181.5907	$181.59	$181.60	$181.60
7 purchase totals =	$880.81		$971.1670	$971.17	$971.15	$971.20