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	$38.58	4.653%	$40.3751	$40.38	$40.40	$40.40
Purchase #2	$160.26	10.383%	$176.8998	$176.90	$176.90	$176.90
Purchase #3	$90.58	13.263%	$102.5936	$102.59	$102.60	$102.60
Purchase #4	$41.65	6.564%	$44.3839	$44.38	$44.40	$44.40
Purchase #5	$168.65	12.401%	$189.5643	$189.56	$189.55	$189.60
Purchase #6	$244.77	11.697%	$273.4007	$273.40	$273.40	$273.40
Purchase #7	$83.98	8.666%	$91.2577	$91.26	$91.25	$91.30
7 purchase totals =	$828.47		$918.4751	$918.47	$918.50	$918.60