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	$115.40	7.268%	$123.7873	$123.79	$123.80	$123.80
Purchase #2	$72.89	8.641%	$79.1884	$79.19	$79.20	$79.20
Purchase #3	$222.85	10.355%	$245.9261	$245.93	$245.95	$245.90
Purchase #4	$127.72	7.220%	$136.9414	$136.94	$136.95	$136.90
Purchase #5	$104.82	3.407%	$108.3912	$108.39	$108.40	$108.40
Purchase #6	$121.63	8.208%	$131.6134	$131.61	$131.60	$131.60
Purchase #7	$237.54	7.519%	$255.4006	$255.40	$255.40	$255.40
7 purchase totals =	$1,002.85		$1,081.2484	$1,081.25	$1,081.30	$1,081.20