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	$115.65	4.523%	$120.8808	$120.88	$120.90	$120.90
Purchase #2	$145.82	3.244%	$150.5504	$150.55	$150.55	$150.60
Purchase #3	$112.76	3.378%	$116.569	$116.57	$116.55	$116.60
Purchase #4	$240.79	8.716%	$261.7773	$261.78	$261.80	$261.80
Purchase #5	$115.73	6.687%	$123.4689	$123.47	$123.45	$123.50
Purchase #6	$116.56	12.737%	$131.4062	$131.41	$131.40	$131.40
Purchase #7	$132.28	11.444%	$147.4181	$147.42	$147.40	$147.40
7 purchase totals =	$979.59		$1,052.0707	$1,052.08	$1,052.05	$1,052.20