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	$40.61	10.588%	$44.9098	$44.91	$44.90	$44.90
Purchase #2	$141.84	8.729%	$154.2212	$154.22	$154.20	$154.20
Purchase #3	$171.37	11.820%	$191.6259	$191.63	$191.65	$191.60
Purchase #4	$86.82	4.415%	$90.6531	$90.65	$90.65	$90.70
Purchase #5	$93.32	10.417%	$103.0411	$103.04	$103.05	$103.00
Purchase #6	$151.35	9.702%	$166.034	$166.03	$166.05	$166.00
Purchase #7	$176.45	4.622%	$184.6055	$184.61	$184.60	$184.60
7 purchase totals =	$861.76		$935.0906	$935.09	$935.10	$935.00