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	$27.86	3.301%	$28.7797	$28.78	$28.80	$28.80
Purchase #2	$217.38	4.648%	$227.4838	$227.48	$227.50	$227.50
Purchase #3	$209.82	6.447%	$223.3471	$223.35	$223.35	$223.30
Purchase #4	$76.86	6.253%	$81.6661	$81.67	$81.65	$81.70
Purchase #5	$129.87	11.220%	$144.4414	$144.44	$144.45	$144.40
Purchase #6	$46.42	12.311%	$52.1348	$52.13	$52.15	$52.10
Purchase #7	$222.29	8.513%	$241.2135	$241.21	$241.20	$241.20
7 purchase totals =	$930.50		$999.0664	$999.06	$999.10	$999.00