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	$105.90	11.804%	$118.4004	$118.40	$118.40	$118.40
Purchase #2	$211.80	3.802%	$219.8526	$219.85	$219.85	$219.90
Purchase #3	$57.81	7.742%	$62.2857	$62.29	$62.30	$62.30
Purchase #4	$59.54	12.648%	$67.0706	$67.07	$67.05	$67.10
Purchase #5	$45.36	3.142%	$46.7852	$46.79	$46.80	$46.80
Purchase #6	$123.30	11.583%	$137.5818	$137.58	$137.60	$137.60
Purchase #7	$100.38	13.466%	$113.8972	$113.90	$113.90	$113.90
7 purchase totals =	$704.09		$765.8735	$765.88	$765.90	$766.00