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	$96.99	6.800%	$103.5853	$103.59	$103.60	$103.60
Purchase #2	$59.63	4.256%	$62.1679	$62.17	$62.15	$62.20
Purchase #3	$150.46	12.619%	$169.4465	$169.45	$169.45	$169.40
Purchase #4	$14.90	13.379%	$16.8935	$16.89	$16.90	$16.90
Purchase #5	$225.42	5.374%	$237.5341	$237.53	$237.55	$237.50
Purchase #6	$138.26	9.578%	$151.5025	$151.50	$151.50	$151.50
Purchase #7	$80.35	7.660%	$86.5048	$86.50	$86.50	$86.50
7 purchase totals =	$766.01		$827.6346	$827.63	$827.65	$827.60