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	$139.59	11.738%	$155.9751	$155.98	$156.00	$156.00
Purchase #2	$91.51	9.554%	$100.2529	$100.25	$100.25	$100.30
Purchase #3	$87.60	10.192%	$96.5282	$96.53	$96.55	$96.50
Purchase #4	$93.48	13.175%	$105.796	$105.80	$105.80	$105.80
Purchase #5	$153.39	13.688%	$174.386	$174.39	$174.40	$174.40
Purchase #6	$99.48	9.464%	$108.8948	$108.89	$108.90	$108.90
Purchase #7	$21.29	11.763%	$23.7943	$23.79	$23.80	$23.80
7 purchase totals =	$686.34		$765.6273	$765.63	$765.70	$765.70