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	$115.59	9.812%	$126.9317	$126.93	$126.95	$126.90
Purchase #2	$205.69	13.278%	$233.0015	$233.00	$233.00	$233.00
Purchase #3	$176.56	13.705%	$200.7575	$200.76	$200.75	$200.80
Purchase #4	$123.31	8.475%	$133.7605	$133.76	$133.75	$133.80
Purchase #5	$29.79	12.828%	$33.6115	$33.61	$33.60	$33.60
Purchase #6	$137.34	9.231%	$150.0179	$150.02	$150.00	$150.00
Purchase #7	$55.58	10.719%	$61.5376	$61.54	$61.55	$61.50
7 purchase totals =	$843.86		$939.6182	$939.62	$939.60	$939.60