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	$52.25	5.234%	$54.9848	$54.98	$55.00	$55.00
Purchase #2	$121.84	12.459%	$137.02	$137.02	$137.00	$137.00
Purchase #3	$20.52	6.760%	$21.9072	$21.91	$21.90	$21.90
Purchase #4	$176.53	12.519%	$198.6298	$198.63	$198.65	$198.60
Purchase #5	$166.28	5.223%	$174.9648	$174.96	$174.95	$175.00
Purchase #6	$139.37	13.433%	$158.0916	$158.09	$158.10	$158.10
Purchase #7	$42.25	3.143%	$43.5779	$43.58	$43.60	$43.60
7 purchase totals =	$719.04		$789.1761	$789.17	$789.20	$789.20