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	$83.87	7.269%	$89.9665	$89.97	$89.95	$90.00
Purchase #2	$118.88	12.404%	$133.6259	$133.63	$133.65	$133.60
Purchase #3	$153.97	11.256%	$171.3009	$171.30	$171.30	$171.30
Purchase #4	$126.69	8.755%	$137.7817	$137.78	$137.80	$137.80
Purchase #5	$69.38	13.554%	$78.7838	$78.78	$78.80	$78.80
Purchase #6	$232.93	13.202%	$263.6814	$263.68	$263.70	$263.70
Purchase #7	$72.27	11.826%	$80.8167	$80.82	$80.80	$80.80
7 purchase totals =	$857.99		$955.9569	$955.96	$956.00	$956.00