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	$215.81	6.206%	$229.2032	$229.20	$229.20	$229.20
Purchase #2	$175.89	6.219%	$186.8286	$186.83	$186.85	$186.80
Purchase #3	$150.82	11.816%	$168.6409	$168.64	$168.65	$168.60
Purchase #4	$87.27	3.852%	$90.6316	$90.63	$90.65	$90.60
Purchase #5	$108.60	4.835%	$113.8508	$113.85	$113.85	$113.90
Purchase #6	$18.98	12.163%	$21.2885	$21.29	$21.30	$21.30
Purchase #7	$44.34	9.207%	$48.4224	$48.42	$48.40	$48.40
7 purchase totals =	$801.71		$858.8660	$858.86	$858.90	$858.80