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	$27.91	3.433%	$28.8682	$28.87	$28.85	$28.90
Purchase #2	$188.49	5.870%	$199.5544	$199.55	$199.55	$199.60
Purchase #3	$126.77	10.370%	$139.916	$139.92	$139.90	$139.90
Purchase #4	$162.42	6.232%	$172.542	$172.54	$172.55	$172.50
Purchase #5	$125.64	6.258%	$133.5026	$133.50	$133.50	$133.50
Purchase #6	$76.60	8.742%	$83.2964	$83.30	$83.30	$83.30
Purchase #7	$209.71	3.409%	$216.859	$216.86	$216.85	$216.90
7 purchase totals =	$917.54		$974.5386	$974.54	$974.50	$974.60