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	$52.98	7.310%	$56.8528	$56.85	$56.85	$56.90
Purchase #2	$248.61	10.138%	$273.8141	$273.81	$273.80	$273.80
Purchase #3	$225.80	5.544%	$238.3184	$238.32	$238.30	$238.30
Purchase #4	$144.69	9.481%	$158.4081	$158.41	$158.40	$158.40
Purchase #5	$243.31	11.197%	$270.5534	$270.55	$270.55	$270.60
Purchase #6	$85.51	10.324%	$94.3381	$94.34	$94.35	$94.30
Purchase #7	$6.63	4.653%	$6.9385	$6.94	$6.95	$6.90
7 purchase totals =	$1,007.53		$1,099.2234	$1,099.22	$1,099.20	$1,099.20