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	$7.57	11.844%	$8.4666	$8.47	$8.45	$8.50
Purchase #2	$93.50	12.752%	$105.4231	$105.42	$105.40	$105.40
Purchase #3	$73.37	3.346%	$75.825	$75.83	$75.85	$75.80
Purchase #4	$215.25	13.605%	$244.5348	$244.53	$244.55	$244.50
Purchase #5	$169.30	9.593%	$185.5409	$185.54	$185.55	$185.50
Purchase #6	$128.95	13.108%	$145.8528	$145.85	$145.85	$145.90
Purchase #7	$57.66	6.218%	$61.2453	$61.25	$61.25	$61.20
7 purchase totals =	$745.60		$826.8885	$826.89	$826.90	$826.80