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	$246.75	13.691%	$280.5325	$280.53	$280.55	$280.50
Purchase #2	$16.54	13.814%	$18.8248	$18.82	$18.80	$18.80
Purchase #3	$241.99	13.846%	$275.4959	$275.50	$275.50	$275.50
Purchase #4	$175.90	7.611%	$189.2877	$189.29	$189.30	$189.30
Purchase #5	$195.27	7.786%	$210.4737	$210.47	$210.45	$210.50
Purchase #6	$56.37	8.737%	$61.295	$61.30	$61.30	$61.30
Purchase #7	$106.89	13.337%	$121.1459	$121.15	$121.15	$121.10
7 purchase totals =	$1,039.71		$1,157.0555	$1,157.06	$1,157.05	$1,157.00