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	$115.54	7.566%	$124.2818	$124.28	$124.30	$124.30
Purchase #2	$184.41	5.677%	$194.879	$194.88	$194.90	$194.90
Purchase #3	$79.33	5.215%	$83.4671	$83.47	$83.45	$83.50
Purchase #4	$44.46	13.618%	$50.5146	$50.51	$50.50	$50.50
Purchase #5	$227.34	5.326%	$239.4481	$239.45	$239.45	$239.40
Purchase #6	$62.84	8.147%	$67.9596	$67.96	$67.95	$68.00
Purchase #7	$90.69	10.308%	$100.0383	$100.04	$100.05	$100.00
7 purchase totals =	$804.61		$860.5885	$860.59	$860.60	$860.60