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	$184.47	3.497%	$190.9209	$190.92	$190.90	$190.90
Purchase #2	$30.50	8.221%	$33.0074	$33.01	$33.00	$33.00
Purchase #3	$58.54	13.421%	$66.3967	$66.40	$66.40	$66.40
Purchase #4	$54.60	3.648%	$56.5918	$56.59	$56.60	$56.60
Purchase #5	$65.65	9.854%	$72.1192	$72.12	$72.10	$72.10
Purchase #6	$169.45	6.176%	$179.9152	$179.92	$179.90	$179.90
Purchase #7	$223.50	5.718%	$236.2797	$236.28	$236.30	$236.30
7 purchase totals =	$786.71		$835.2309	$835.24	$835.20	$835.20