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	$248.45	12.771%	$280.1795	$280.18	$280.20	$280.20
Purchase #2	$64.47	12.314%	$72.4088	$72.41	$72.40	$72.40
Purchase #3	$145.67	3.535%	$150.8194	$150.82	$150.80	$150.80
Purchase #4	$72.47	4.442%	$75.6891	$75.69	$75.70	$75.70
Purchase #5	$41.73	4.595%	$43.6475	$43.65	$43.65	$43.60
Purchase #6	$54.40	13.503%	$61.7456	$61.75	$61.75	$61.70
Purchase #7	$233.50	10.577%	$258.1973	$258.20	$258.20	$258.20
7 purchase totals =	$860.69		$942.6872	$942.70	$942.70	$942.60