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	$79.39	11.113%	$88.2126	$88.21	$88.20	$88.20
Purchase #2	$231.67	5.704%	$244.8845	$244.88	$244.90	$244.90
Purchase #3	$249.46	12.613%	$280.9244	$280.92	$280.90	$280.90
Purchase #4	$156.64	12.703%	$176.538	$176.54	$176.55	$176.50
Purchase #5	$25.39	11.396%	$28.2834	$28.28	$28.30	$28.30
Purchase #6	$48.48	8.314%	$52.5106	$52.51	$52.50	$52.50
Purchase #7	$84.45	6.494%	$89.9342	$89.93	$89.95	$89.90
7 purchase totals =	$875.48		$961.2877	$961.27	$961.30	$961.20