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	$94.59	5.325%	$99.6269	$99.63	$99.65	$99.60
Purchase #2	$82.50	12.172%	$92.5419	$92.54	$92.55	$92.50
Purchase #3	$121.50	12.239%	$136.3704	$136.37	$136.35	$136.40
Purchase #4	$5.53	6.228%	$5.8744	$5.87	$5.85	$5.90
Purchase #5	$71.46	9.860%	$78.506	$78.51	$78.50	$78.50
Purchase #6	$187.46	5.725%	$198.1921	$198.19	$198.20	$198.20
Purchase #7	$138.41	10.832%	$153.4026	$153.40	$153.40	$153.40
7 purchase totals =	$701.45		$764.5143	$764.51	$764.50	$764.50