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	$28.32	10.742%	$31.3621	$31.36	$31.35	$31.40
Purchase #2	$59.59	3.178%	$61.4838	$61.48	$61.50	$61.50
Purchase #3	$142.36	8.695%	$154.7382	$154.74	$154.75	$154.70
Purchase #4	$141.76	7.639%	$152.589	$152.59	$152.60	$152.60
Purchase #5	$123.39	10.295%	$136.093	$136.09	$136.10	$136.10
Purchase #6	$16.97	12.181%	$19.0371	$19.04	$19.05	$19.00
Purchase #7	$245.39	13.829%	$279.325	$279.33	$279.35	$279.30
7 purchase totals =	$757.78		$834.6282	$834.63	$834.70	$834.60