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	$249.98	12.155%	$280.3651	$280.37	$280.35	$280.40
Purchase #2	$120.34	5.368%	$126.7999	$126.80	$126.80	$126.80
Purchase #3	$102.30	13.289%	$115.8946	$115.89	$115.90	$115.90
Purchase #4	$64.33	12.758%	$72.5372	$72.54	$72.55	$72.50
Purchase #5	$88.68	5.788%	$93.8128	$93.81	$93.80	$93.80
Purchase #6	$246.40	3.824%	$255.8223	$255.82	$255.80	$255.80
Purchase #7	$250.52	11.709%	$279.8534	$279.85	$279.85	$279.90
7 purchase totals =	$1,122.55		$1,225.0853	$1,225.08	$1,225.05	$1,225.10