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	$249.50	12.375%	$280.3756	$280.38	$280.40	$280.40
Purchase #2	$153.96	6.750%	$164.3523	$164.35	$164.35	$164.40
Purchase #3	$39.61	5.752%	$41.8884	$41.89	$41.90	$41.90
Purchase #4	$151.47	12.472%	$170.3613	$170.36	$170.35	$170.40
Purchase #5	$165.39	11.713%	$184.7621	$184.76	$184.75	$184.80
Purchase #6	$100.34	12.163%	$112.5444	$112.54	$112.55	$112.50
Purchase #7	$23.27	3.781%	$24.1498	$24.15	$24.15	$24.10
7 purchase totals =	$883.54		$978.4339	$978.43	$978.45	$978.50