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	$38.75	5.382%	$40.8355	$40.84	$40.85	$40.80
Purchase #2	$237.26	8.798%	$258.1341	$258.13	$258.15	$258.10
Purchase #3	$42.39	12.661%	$47.757	$47.76	$47.75	$47.80
Purchase #4	$204.89	8.405%	$222.111	$222.11	$222.10	$222.10
Purchase #5	$165.67	9.208%	$180.9249	$180.92	$180.90	$180.90
Purchase #6	$63.63	4.848%	$66.7148	$66.71	$66.70	$66.70
Purchase #7	$37.80	7.156%	$40.505	$40.51	$40.50	$40.50
7 purchase totals =	$790.39		$856.9823	$856.98	$856.95	$856.90