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	$249.81	13.800%	$284.2838	$284.28	$284.30	$284.30
Purchase #2	$238.64	6.796%	$254.858	$254.86	$254.85	$254.90
Purchase #3	$138.33	8.499%	$150.0867	$150.09	$150.10	$150.10
Purchase #4	$44.59	6.102%	$47.3109	$47.31	$47.30	$47.30
Purchase #5	$109.74	4.704%	$114.9022	$114.90	$114.90	$114.90
Purchase #6	$59.60	11.243%	$66.3008	$66.30	$66.30	$66.30
Purchase #7	$114.83	13.679%	$130.5376	$130.54	$130.55	$130.50
7 purchase totals =	$955.54		$1,048.2800	$1,048.28	$1,048.30	$1,048.30