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	$139.40	4.286%	$145.3747	$145.37	$145.35	$145.40
Purchase #2	$135.96	3.803%	$141.1306	$141.13	$141.15	$141.10
Purchase #3	$99.37	11.801%	$111.0967	$111.10	$111.10	$111.10
Purchase #4	$232.68	13.527%	$264.1546	$264.15	$264.15	$264.20
Purchase #5	$39.64	9.764%	$43.5104	$43.51	$43.50	$43.50
Purchase #6	$106.84	13.343%	$121.0957	$121.10	$121.10	$121.10
Purchase #7	$40.89	5.540%	$43.1553	$43.16	$43.15	$43.20
7 purchase totals =	$794.78		$869.5180	$869.52	$869.50	$869.60