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	$247.33	13.403%	$280.4796	$280.48	$280.50	$280.50
Purchase #2	$114.59	10.704%	$126.8557	$126.86	$126.85	$126.90
Purchase #3	$154.35	4.796%	$161.7526	$161.75	$161.75	$161.80
Purchase #4	$81.39	9.799%	$89.3654	$89.37	$89.35	$89.40
Purchase #5	$235.48	6.284%	$250.2776	$250.28	$250.30	$250.30
Purchase #6	$58.86	6.658%	$62.7789	$62.78	$62.80	$62.80
Purchase #7	$57.94	9.817%	$63.628	$63.63	$63.65	$63.60
7 purchase totals =	$949.94		$1,035.1378	$1,035.15	$1,035.20	$1,035.30