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	$236.89	7.571%	$254.8249	$254.82	$254.80	$254.80
Purchase #2	$83.86	11.479%	$93.4863	$93.49	$93.50	$93.50
Purchase #3	$224.88	13.560%	$255.3737	$255.37	$255.35	$255.40
Purchase #4	$249.65	12.451%	$280.7339	$280.73	$280.75	$280.70
Purchase #5	$157.99	11.796%	$176.6265	$176.63	$176.65	$176.60
Purchase #6	$137.39	5.786%	$145.3394	$145.34	$145.35	$145.30
Purchase #7	$41.98	4.625%	$43.9216	$43.92	$43.90	$43.90
7 purchase totals =	$1,132.64		$1,250.3063	$1,250.30	$1,250.30	$1,250.20